Immediately prior to the outbreak of the war in 1939, Perkins were in discussion with the Government to develop a large diesel engine for use in small naval craft such as Air/Sea Rescue, Gun Boats and Torpedo Boats in substitution for the petrol engines then used. The engine was needed to produce up to 1000 BHP and to fit in the same space as the Rolls Royce Merlin, which was beginning to be fitted in these fast boats, but the priority need was for aircraft.

Perkins response was to produce the T12 engine, the last product to be designed by Charles Chapman. The engine went from first design concept to initial prototype running in about 14 months, in spite of the difficult wartime conditions, supply restrictions and the very small engineering team working on it.

The engine is a 55-degree vee, with twelve cylinders of 6 inch bore and stroke. The resultant capacity of 33,3 litres makes this the largest engine designed and produced at the Peterborough factory, and at over two tons also the heaviest. There are a number of unusual design features including the use of a centrifugal supercharger driven from the crankshaft nose through step-up gearing. The engine was deliberately designed as two six-cylinder engines driving a common crankshaft, so that in the event of a failure in one bank, the engine could still function on the other! Thus each bank has independent water, oil and fuel injection pumps. Each cylinder has a separate cylinder liner, water jacket and cylinder head, bolted to a common crankcase. There are twin inlet valves and one exhaust valve in each cylinder, with indirect injection using the ‘Aeroflow’ combustion chamber as made famous in the ‘P6’ engine. The systems included sea-water cooled air charge coolers for each bank.

Only five or six of these engines were ever made, and two were used for sea trials in a Royal Navy launch, ML570, from about the end of 1942 until after the end of the War.

Performance development work eventually achieved the 1000 BHP required and the engine showed reasonable reliability, but the availability of cheap American petrol engines reduced the need for the engine, so that no production order was placed.

This display engine is now the only one left and had been used to power an emergency generator set at the Eastfield factory until the 1980s.

Notes by David Boulton April 2006