"One of the most curious beer terms is the use of the word "bomber" being used to refer to the 22oz bottle package format. Although this bottle size has been around since the pre-prohibition era, the origin of the term isn't as clear. Many attribute the nickname "bomber" to the B-22 Bomber Aircraft. But in actuality, this obscure model never went into production and was simply a design upgrade on the B-18 model that never got off the ground (no pun intended). Other beer historians cite the possibility that the term is an adaptation from the "bumper" bottle terminology borrowed from England, where it was used more generally to refer to any beer bottle larger than a normal serving."
Bombers are specifically 22 fl oz bottles. Not quite sure about the etymology, but maybe it has something to do with that size beer getting one "bombed" or "blitzed"