In 1844 he replaced the engines of the Admiralty yacht, HMS Black Eagle with oscillating engines of double the power, without increasing either the weight or space occupied,[3] an achievement which broke the naval supply dominance of Boulton & Watt and Maudslay, Son & Field.
[2] His enhanced reputation due to this notable advancement was further augmented by Penn's introduction of trunk engines for driving screw propellers in vessels of war.
[2] These advancements were coupled with a reputation for quality and reliability and this led to Penn becoming the major engine supplier to the Royal Navy as it made the transition from sail to steam.
[2] Penn was also responsible for introducing wood bearings for screw-propeller shafts which became vital to the worldwide use of steam-powered ships.
Built (or assembled) in 1861, it is the only known example, and in being recovered intact was found to have all its fittings and fixtures attached including Penn's nameplate.