RUSI research fellow Justin Bronk has made the case for replacing the RAF’s Sentinel R.1 fleet with additional P-8A Poseidon aircraft.

Justin Bronk is a Research Fellow specialising in combat airpower and technology in the Military Sciences team at RUSI. He is also Editor of the RUSI Defence Systems online journal.

The Sentinel R1 is an airborne battlefield and ground surveillance aircraft and is interoperable with other allied systems such as JSTARS and the NATO Alliance Ground Surveillance system. In 2010 the UK government’s Strategic Defence and Security Review announced its intention to “withdraw the Sentinel airborne ground surveillance aircraft once it is no longer required to support operations in Afghanistan”.

Sentinel has supported the British Army in Afghanistan and allied efforts in Libya and other locations. This was reversed in the last defence review, which stated:

“Sentinel will be extended in service into the next decade; Shadow until at least 2030; and Sentry and Rivet Joint until 2035.”

Bronk discusses the multiple retirement dates given for the type and why that’s an issue:

“Unfortunately, there have been several negative consequences of the multiple retirement date announcements and postponements for the Sentinel fleet. First and foremost, long-term investment requirements such as training simulator upgrades and base infrastructure components have been difficult to resource due to constantly looming official out-of-service dates.

Sentinel in flight over Iraq.

The aircraft themselves have been upgraded and overhauled as mission tempo and changing real-world missions required, but without a standardised and sustainable structure in place for the Sentinel ecosystem as a whole.”

The P-8 Poseidon, developed by Boeing, is designed to conduct anti-submarine warfare (ASW), anti-surface warfare (ASUW), and shipping interdiction, along with an electronic signals intelligence (ELINT) role. This involves carrying torpedoes, anti-ship missiles and other weapons. The type is also capable of overground surveillance.

Bronk goes on to explain why expanding the P-8 fleet is a good idea within the context of replacing Sentinel.

“It is thus a fair assumption that the RAF’s P-8A Poseidon fleet will find itself heavily utilised, and with only nine aircraft there will be an inherent and inescapable trade-off between the capacity and crew proficiency for the core (and critical) ASW mission set, and other global surveillance and enabler missions. This brings us to the central point.

Image Crown Copyright 2020.

If the UK can buy its way into the highly capable AAS radar programme, which is not a certainty but there are multiple historical precedents for, then the RAF could replace the remaining Sentinel R.1s one for one with additional P-8As equipped with the AAS pod. This would ensure that the Sentinel’s valuable wide-area surveillance, SAR mapping and GMTI capabilities are not lost during the cuts which are likely as the global economy contracts post coronavirus, when small bespoke fleets of enabler aircraft will be the juiciest targets.”

You can read the full article here.

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For a further explanation of the P8 fitted with the Advanced Airborne Sensor (AAS), see the below link. The US Navy P8s have been testing the AAS since last year. Although they are being tight lipped about its capabilities, the US Navy are very happy with its development. There was one report of the system being used to track drug running boats and semi-sermersible craft in the Gulf of Mexico. The burning question though is it at least on par with Sentinel, if not why bother? From the cyptic answers and reading between the lines, it appears that the… Read more »


Looks like a great capability boost. I wonder if we could have some of our later fleet equipped in their build phase as surely that would cost less than adding it on later, that’s if we even decide to equip ours with this secretive ( prob costly) tech.


The AAS is made by Raytheon. It’s from the same family of radars that the Sentinel radar is from.
The big issue would be what about ground stations, handoff to targets etc. that Sentinel is really good at.


I agree with much of what you wrote apart from using the 737. Let me explain first with the current pandemic many airlines are getting rid of their larger aircraft such as the A380. Would that not be an ideal aircraft as a networking hub for unmanned vehicles and possibly a communication hub for our and or US SSBNs such as the E6B Looking Glass. The aircraft would be relitivly cheap to buy as airlines don’t want them, Ive seen pricies as low as £50 million, they are relitivly modern so would have many years left in them and as… Read more »


Nice idea, but i think we all know what will happen is that they will announce that the capability of the sentinel is now provided by the P8 and that that as the P8 is a better overall platform and can do the job of multiple sentinels, sentinel is no longer needed. Its 101 in the MOD capability cut excuses playbook.

Steve H

All interesting points here, there’s a definite conflict of interest with the Sentinel, River Joint, Sentry and then the P-8 Poseidon. Its like a “rob Peter to pay Paul” type of conundrum and its not a decision I’d like to make..

Nigel Collins

A very good idea when you consider the range of weapons it will carry.

“US Navy plans to arm P-8A with cruise missiles, bombs, sea mines and decoys”


I like this idea. Commonality of types is something everyone on here gets and likes.
But the additional sensor and comms packages that the US and (I think) Australia are bringing in for their P-8As makes this a really smart idea. It would supplement our Wedgetail order nicely, in my view.


Too sensible plan for MOD to adopt; plus it wasn’t their idea. No chance.


Out of interest how much commonality is there between maritime and overland missions regarding operator skills/training for people on the consoles at the back? Is it exactly the same skill set so that someone who has been out hunting subs in the North Atlantic since signing up could transfer over to doing ground surveillance in Afghanistan or wherever the next major land operation happens to be with no extra training or is there some minor/modest/significant retraining needed to adapt from a marine to land environment or vice versa? I can see the big benefits from equipment and pilot commonality but… Read more »

David Flandry

The Nimrod Mk2 was used in some of these overland roles in Afghanistan, including recce and elint. There was even informed discussion about using it for bombing roles.

Sean Crowley

No , Chalk and Cheese , you guys have an invaluable asset with the Sentinel , it does more than just paint pretty landscape pictures , it is real time battle assessment C2 asset, i have seen what the Americans can do with they’re E-8C and have been led to believe the UK has close to the same ability with this platform . Were talking about monitoring vast areas with high resolution fixed target imagery that then can be alternated with MTI that gives you real time eye in the sky intel irrespective of conditions that would make higher EM… Read more »


A squadron based in England, or even for the Royal Navy would be good, based in south west uk.


Not sure. I worry that the P-8 is a big target to fly over the battlefield. I am not a fan of unmanned, but for this task it might be better to have a stealthy drone.
I think the 9 RAF P-8 need stand off weapons such as LRASM & SLAM-ER.

Steve H

That’s a good point mate, having this capability on a P-8 gives the platform another string to its bow if you know what I mean, it makes the aircraft an even more dangerous animal in the maritime role. As the P-8 has long range sensors, it could attack enemy naval assets using long range stand off weapons without having to expose itself to likely anti aircraft defence systems.


This plan would make sense to me, assuming there was no dramatic loss of capability. The sentinel, as great as a platform as it appears to be, has been vulnerable for years now and there are good points made about sustainability into the future. More P8s with interchangeable pods will secure the capability and give the P8 fleet some more critical mass. I’m not sure how many P8s are in use at any given time (2 on ops during high intensity periods?), but drawing from a larger pool of P8s has to be more efficient. Could they all be based… Read more »


I meant sentinels on ops at any given time


Kinloss next door would be the best option, however the south west uk should have them based there to cover that area of the Atlantic but for all maintenance ect they should go to Lossiemouth.


with the ISTAR capability, Waddington would be the logical choice as it is INSTAR centre of universe. I do agree with a SW satellite station, likely st mawgan as I think too much is at Lossie right now. I usually get shot down when I discuss St Mawgan. Loads of room there now since Cornwall airport is dead as a concept

Steve H

It makes sense to deploy the aircraft around the British Isles so they can cover a wider area quickly, it would also cut down flying hours meaning less maintenance. If they were all at Kinloss say, it would take about 2 hours to fly to an incident off of the Cornwall coast which would burn fuel before they even got on station. Also, there’s the old “too many eggs in one basket” thing to think of.

Steve Salt

St Mawgan’s still there in the guise of Newquay /Cornwall airport but I doubt reactivation is a possibility but HMS Seahawk at Culdrose could do the job, perhaps even giving the aircraft an RN squadron moniker.


The Brits and the Aussies are probably the only countries that the U.S. would even consider giving this advanced capability too. The only capabilities the Brits would lose with this and the P-8 would be some endurance and a lower altitude. But they would be getting a vastly more advanced and capable radar.

John Clark

I agree with the group, add a batch of additional P8’s to our 9 currently under contract.

Sentinel is a fantastic asset, but like the scrapped Nimrod MR4A, it’s a tiny bespoke fleet.

Modern avionics require regular technology refresh and rhe cost of this can end up being enoumous.

So absolutely buy the bolt on kit for the P8’s and another 4 or 5 airframes.


4 to 5 P8s with AAS is more expensive than sentinel until 2035


India and lots more nations have bought the P8 actually.


But those P8’s do t have the AAS


So we need an extra 8 p8s To cover all the tasks we will need them to do in future according to a report into the numbers. And to also replace sentinel say 6, so an order of 14 extra will be needed, can’t see that happening unfortunately but no surprise there. Atleast we are also getting wedgetails to replace our old awacs fleet so we will have a pretty new fleet. Not sure what will replace rivet joint in future, actually it’ll prob be what ever the USA decides they will replace with.

Meirion X

We be lucky to get a extra 3 P8s, I think?


We’ll be lucky to get AAS pods for the existing 9 P-8’s to replace the capability lost as Sentinel is chopped. Even if we get AAS there’ll certainly be a capability gap between losing Sentinel. The cost of Covid-19 runs into hundreds of billions and the treasury will want to claw it back.

John Clark

Probably a handful, I would imagine they procured 5 Sentinels to to keep three available.

Using that logic, they will probably sanction an additional 3, we would be very lucky to get 5.

What’s needed is a fleet of 25, (18 covering all tasks, with 7 maintenance, training etc).

This would allow forward basing of assets, based in Cyprus and the middle East.

In the right numbers, the P8 becomes a real force multiplier.


When the bill for Covid-19 comes in we’ll be lucky to get AAS pods for the existing 9 P-8’s while Sentinel will be chopped. Anyone thinking we’re going to get many more P-8’s is delusional.
It’s going to be a blood bath with the treasury for all departments and defence is an easy one to chop.


Given that the BoE is now able to sell Government Bonds with negative rates carrying the extra debt from Corvid-19 isn’t an issue. We’ll still have less debt by GDP% than we had in the 1960’s.

Meirion X

How come you still a taxpayer at 76 years old?

Meirion X

So you are not a Communist then?
Mind you, I have heard of a ‘Champagne Socialist’!

Meirion X

Have you not heard of Keynesian?

If you had, you would be advocating investments in infrastructure including defence infrastructure which would benefit the economy all round. Not sprouting simplistic BS economics of austerity headlong of the oncoming recession.

Meirion X

Essentially your comment is just bull s**t austerity economies convenient for peacenacks!

John Clark

Who are you arguing with Mention?

Meirion X

With Harold, John.


That’s why you don’t understand, you think a person that favours defence spending is pro-war so you ask if they’ve killed someone as if that’s a prerequisite to disagree with you. You’ve just proved you don’t understand defence is an investment in peace. That’s why its called defence not offence, your thinking doesn’t allow you to understand the dangers of allowing opportunity to potential aggressors, it’s an open invitation to them to disarm. The world is more dangerous now than anytime since the end of the cold war as nationalism and authoritarianism reappear and post covid-19 that’s likely to get… Read more »


As a datapoint, even after these massive Covid-19 rescue packages (which in my view have been handled well -Rishi Sunak is a star of this show I think), here is some historical context – Net UK debt after all the Covid-19 spending is currently estimated to rise to a bit over 100% of GDP before maybe dropping to 95% of GDP in 2021. After WW2 we just about hit 240% of GDP for our national debt; we actually entered WW2 with a national debt of 140% of GDP due to the great depression and overhang from WW1. Going back… Read more »


I think after 2008 austerity was required not due to the level of debt but due to the annual deficit. The U.K. due to its large financial sector was disproportionately affected by the 2008 crash. (The coincidental Eurozone crisis was a totally different issue that was catalysed by the financial crash and the resulting drop in liquidity. And some countries, weren’t affected by 2008 at all, eg Australia.) This crisis by comparison is global crisis and so can be handled differently. Sunak has played a blinder in protecting the economy so far. And the eagerness with which UK Government Bonds… Read more »

Meirion X

I agree with your comment, Graham!

Meirion X

“Incidentally, I made my money without involvement with the arms trade… “. So you bite the hands of those whom feed and defend you?

Meirion X

So, you made your money under the protection of the British state then?
So who else would of protection you then?


A potential problem of mission creep here. Currently our few P8’s already have an excellent ISTAR suite, with the addition of the littoral pod the USN are experimenting with, it truely would become an excellent replacement… if the system can be developed for more than just littoral (coastal) operations as the USN intends it for. However, then you’d have the issue of having our MPA becoming stretched as they do other duties away from their main maritime role; much like the Nimrod MR2’s in their late life. Unless we have the airframes and crews, we could see this happening again,… Read more »

John Clark

Absolutely Mike, my greatest fear would be the replacement of Sentinel with three P8 pods and no additional airframes or crew!

The bean counters would push very hard for this…


Spot on about one thing: big cuts on the way…….

Meirion X

Have you not heard of Keynesian Economics?

If you had, you would be advocating investments in infrastructure including defence infrastructure which would benefit the economy all round. The Bull s**t economics of austerity is No solution to this oncoming recession. We need to learn the lessons of aftermath of World War 2!

John Clark

I’m curious why you think (so called) austerity is bull shit Motion? I say ‘so called’ because we still spent more than we earned, every year since 2010. It’s a simple economic fact that you can’t continually spend and borrow more than you earn. You can’t live beyond your means. If you do, the interest on debt accrued will become crippling and the burden passed onto the next generation to pay back… Unfortunately, after this economic carnage, we will have no choice but to borrow heavily, we better hope those in charge spend it wisely on economic development, because our… Read more »


We can totally live beyond our means, just keep printing money brrrrrr.

Meirion X

So, how did Britain dig it’s way out of a 250% of GNP war debt burden post WW2?

Meirion X

I should of been 240% of GNP at the time, but still very significant.


“I’m curious why you think (so called) austerity is bull shit Motion?” That’s because it’s been proven that the policy of austerity actually stunted growth, which itself is a far healthier way to reduce the deficit, the architect of austerity has been discredited after their economic modelling was done again, and the head of the IMF actually apologised a few years ago for advising countries to use austerity right after the crash Not to mention the second recession it caused for us the US and eurozone in 2011/12, another recession so quick after such a long and hard one in… Read more »

John Clark

Motion should read Meirion Sole, bloody predictive spelling! We seem to keep discussing this Sole, there are (were) two ways to look at the economy, from the left or the right. One advocates spending no matter whats in the bank, in the hope that the growth is created in the economy, in a tail wagging the dog sort of way. the other advocates spending within strict fiscal limits set by GDP and related borrowing within clearly defined credit limits to control the interest that needs repaying. As we have said before though Sole, this is all now utterly irrelevant, the… Read more »

Meirion X

I accept your apologies, John for my misspellt name. And Sole has mainly answered my reply.

John Clark

Sorry about the auto correct, my phone has a bloody annoying habit of auto, auto correction, even when I go back and change it!

We are all entitled to our political and economic personal views, fact is, it really is now irrelevant.

We are facing a future, were we we will be borrowing and spending like a teenager with a credit card!

Meirion X

But if only the government borrows money from it’s own citizens, in the way of National Savings or by Gilt Edge by Pension Funds, the Nation is more or less owed itself. Also some of the interest received by citizens will be taxable.

Glass Half Full

John, others have provided responses regarding the negatives of austerity so I’ll comment on a couple of other points. Its a mistake to think about the financing of countries as you would personal finance, especially G7 countries. Japan national debt has been >100% of GDP since the late 90’s and >200% since 2009. In 2019 it was >250%. Interest rates are extremely low currently. To quote from Reuters “The UK Debt Management Office (DMO) just sold 12 billion pounds of the 0.375% October 2030 gilt, part of 225 billion pounds of debt issuance planned between April and July to fund… Read more »


U.K. Gov Bonds of shorter terms are actually now at negative yields. The U.K. is scene as safe place for investors to shelter their money so are prepared to take a hit like this.


Current U.K. Government Binds are selling with negative yields. Effectively the government is being paid by investors to take their money. So interest won’t be an issue.

John Clark

I think we will sadly need a robust defence more than ever once this is over. Covid19 will run unchecked in many parts of the world, probably causing yet more instability and losses. The gap between the haves and have nots, will be even more stark, those with health care and those without, not just in the third world, but in the US, were poor people will/are simply being thrown to the wolves it would seem. I wouldn’t be surprised to see half a million dead in the US before a vaccine is widely available. Expect civil unrest aplenty….. All… Read more »

John Clark

Harold, I think we need a robust ability to project power, we have worldwide defence commitments, as part of NATO and as a newly indipendant country, we need to protect our lines of supply and be prepared to assist trading partners. That said, Clearly our involvement in Iraq, Afghanistan and Libya were highly questionable, achieved little and left things worse than they were. I absolutely agree that if we expect our youngsters to give their lives for their country, it had better be for a bloody good reason, with a clear justified mission and exit strategy. The forthcoming defence review… Read more »


No Harold, Libya was going to be a blood bath as Gaddafi would’ve slaughtered half the country to hang on to power. It’s not a blood bath now as you called it, yes there’s factional fighting and the country is not united perhaps it can’t survive as a unitary state but that doesn’t mean we weren’t correct to intervene. You say you dread to think what will happen with Turkey well in 2013 we refused to back the SDF and as a consequence Putin realised the door was open as we would not intervene and the results are what you… Read more »

r cummings

Very well put Graham and I fully agree. If the civilised countries do nothing, dictators, ideologues, power-hungry politicians et al will happily nvade their neighbours, commit genocide, bomb their own people and breach each and every tenet of international law. Intervention may be wholly successful (Gulf War 1, Falklands, Kosovo), partly successful (Bosnia, Libya, Iraq) or not very successful (Afghanistan). But that is a heck of a lot better than watching mass genocie in Rwanda, the slaughter of civilians in Syria, the seizure of territory by force in Crimea, Ukraine and Georgia. We learned the high price of inaction in… Read more »


All it takes for evil to prosper is for good men to stand by and do nothing.

Rob Young

I’m not sure how relevant this is. During WW2 defence expenditure was massive and we had a lot more stuff than needed under any peace time circumstances. Further, the Empire was gradually lost so fewer commitments anyway. I don’t see any evidence of massive defence spending over the norm in the last six years or so, nor do I see a reduction in need.

John Clark

Previous cuts have already hollowed out our defence capability, there is little left to cut.
Challenger2 perhaps …. Albion and Bulwark and one of the carriers, with a trimmed Royal Marines ??
Is there anything else the bean counters could attack really, everything else is cut to the bone.

Rob Young

I agree – my comment was in reply to Harold and his WW2 cuts comment – not relevant to the current situation. And my own view is that we need more, not less, military spending, but concentrated more on the RN surface fleet.

Meirion X

Actually, defence spending increase a lot a few years later due to the Korean War.

Meirion X

Yes defence expenditure was cut immediately after the end of WW2, but caused a recession before the economy could be restructured from war time production to a market economy, and for
reconstruction could begin, which was held back due to shortages of materials etc.


The radar on the E7 has some capability here,MTI and could be further developed with the Aussies,a compromise but money’s going to be a problem whatever.


It was once mentioned that P-8A production is limited by the availability of 737-800 airframes; which are not in production. Production was going to be wound up by early to mid 2020s as a result. New orders means new airframes. Will Boeing accept new orders?

Rob Collinson

This sounds like common sense. Adding to a currently running programme will be cheaper than setting up a new one one. Also slows for economies of scale with currently building up P8 and then E7 lines based on the same base aircraft. It will also fit better with the economic issues post Covid-19.


Doesn’t sound like any sense to me. If the government was willing to spend the money to keep the capability they wouldn’t scrap the Sentinel in the first place.

Sceptical Richard

Crazy to get rid of Sentinel


If the government was willing to spend the money to keep the capability they wouldn’t scrap the Sentinel in the first place.