The Ministry of Defence is asking industry to design affordable, single-use engines for munitions and one-way attack systems, in a tender that addresses one of the key components behind the low-cost strike weapons the Defence Investment Plan commits Britain to fielding at scale.
Project CALLISTO, published on the government’s Contracts Finder on 6 July by Defence Equipment and Support at Abbey Wood, seeks “affordable, single use engines for current and future air systems, munitions and One Way systems, to bridge the performance gap between hobbyist, model aircraft engines and higher performance, long-life and more exquisite engines.”
The £750,000 contract covers the design, development and ground testing of four prototype engines, which the tender states “must be affordable and scalable,” with any future scaled production excluded from this competition and subject to separate procurement if required.
The requirement is split into two lots, with tenderers able to bid for one or both. CALLISTO LIGHT covers a smaller engine producing 750 newtons of thrust, while CALLISTO HEAVY covers a more powerful engine in the 1.8 to 2 kilonewton class, thrust ranges associated with target drones, one-way effectors and small cruise missiles. The competition closes at noon on 27 July, with the contract running from 16 October 2026 to 31 March 2027 under an open below-threshold procedure that the notice marks as suitable for small and medium-sized enterprises.
Conventional cruise missile engines are precision-built for reliability and long shelf life, and their cost and production rate constrain how cheaply and quickly the weapons around them can be made, while hobbyist-grade engines lack the performance and consistency that a military munition requires. An engine designed from the outset to be thrown away after a single flight can dispense with the durability and much of the cost that a reusable powerplant demands, and the war in Ukraine has seen both sides field one-way weapons in the thousands built around exactly this class of propulsion.
