In 1940-41, the Australian war effort had no suitable engine to power its AC3 Thunderbolt tank, so it created one—using three American Cadillac V8s lashed together.

This oddball powerplant, and the circumstances that led to its creation, will remind you of a previous feature we did here at Mac’s Motor City Garage on the Chrysler A-57 tank engine (see the story here). Desperate for engines to power the U.S. Army’s Sherman M4 tanks, Chrysler engineers lashed together five inline-six automobile engines to produce a 30-cylinder power unit. In a similar way, Australian engineers on the other side of the world at around the same time used multiple passenger-car engines to power its AC-3 Thunderbolt tank, but here they combined three Cadillac V8s from the USA in a single power module.

The Perrier-Cadillac unit, named for engineer Robert Perrier, used three standard production L-head Cadillac V8s as used in the 50 through 75 series passenger cars. (This was the first monobloc Cadillac V8 introduced in 1937.) With 346 cubic inches and 135 hp each, the three combined V8s displaced 1039 cubic inches and produced a rated 397 hp. A common crankcase fabricated from heavy steel plate (above left) allowed the three V8 blocks to be bolted together at their oil pan rails in a delta formation, with a transfer case at the rear of the engines (above right) to drive a common output shaft.

This three-in-one V8 arrangement, a WW-24 if you will, was actually an improvement on an earlier setup for the AC1 Sentinel tank, the Thunderbolt’s predecessor, that used three Cadillac V8s combined in a bulky cloverleaf configuration. The power units were assembled at the General Motors Holden division in Melbourne, Australia.

The program initially received approval to produce 200 tanks, but by July 1943 the Australian military was receiving a sufficient supply of U.S. and British tanks and the contract was cancelled. The single prototype still exists today at the Australian War Memorial in Canberra.