Cadillac V16
Clearest image ever taken of Mercury
Harley-Davidson model LR-64 rocket engine, built for the US Navy to power unmanned target drones. This deceptively small (only 21" long) liquid fueled rocket engine was capable of pushing the AQM-37 Jayhawk target drone to which it was attached along at supersonic speeds. One high-performance variant of the drone managed to hit Mach 4.7 during testing! That's absolutely booking it when you consider that Lockheed's (manned) SR-71 Blackbird was "only" able to do about Mach 3.5 flat-out.
This engine was originally designed by Rocketdyne, but the very same bar-and-shield company known more for its motorcycles than rocket engine expertise also had a hand in production. The rocket engines were built during Harley-Davidson's AMF-ownership years, with rocket engines and complete motorcycles both leaving HD's York, PA plant side by side. Over 5000 engines in total were built, although obviously they were intended to be (mostly) disposable, so many didn't survive.
There are a couple of these engines at the Wheels Through Time museum in Maggie Valley, NC. They don't look like much sitting still in a glass case, but in this instance, looks can be deceiving. These particular hogs, can-in fact, actually fly!