2:55 PM
Today's interesting bit of history, from online research into B-17s during WWII, on which my grandfather served as a gunner. Reading up on the .50 caliber machine guns on B-17s, I found this page:

The machine gun fired at a rate of 550 rounds per minute - however - some enterprising gunners found a way to increase their fire power! The red fiber disks in the back plate were of the exact same size as an American quarter - a 25 cent piece - which became valuable in a machine gun. The fiber disks were replaced with American quarters. It required ten dollars worth of quarters to replace the fiber disks in the back platte of each gun. The hardness of the silver coins caused the recoil of the bolt to react quicker - increasing the machine gun fireing rate from 550 rounds to 650 rounds per minute. A gunner so altering the gun in this manner had to be very careful when in combat such that he could overheat his gins much faster than with the fiber disks ! But - the increase in fire power was worth it when enemy fighters made a pass at the formation - and the pass usually lasting on 15 to 30 seconds ! The silver quarters would compress from the beating of the rearward force of the steel bolt - thus the gunner had to always check the quarters for size and replace them when necessary. Necessary being estimated at about every ten combat missions.

As with many WWII topics, once you start looking there's an incredible wealth of fascinating material to read--from how to ditch from a B-17 in a water landing (and the Goldfish Club, with the matching Caterpillar Club for bailing out) to the fantastic array of names given to the aircraft.