Amidships (noun, plural) are ships that navies in most countries use as bases for sailors who have never learned to fire a weapon accurately. (see amid)
Navies feel that if they simply toss these poor-shooters out of the navy then the navies would be 1) admitting that the navy failed in its attempts to properly train the sailors on how to shoot and 2) giving enlisted sailors who change their minds or, in the time of a draft, draftees who never wanted to be in the navy in the first place an easy way out of serving. Rather than doing that, navies assign their aimless shooters to ships that will never see active duty, i.e. amidships.
Whenever the fleet of amidships gets overcrowded, rather than commissioning new ships or, perish the thought, discharging sailors who can’t learn to shoot straight, the navy simply declares that it’s time for target practice to hone the sailors’ skills. The inevitable deaths of people standing way out of the line of fire to the bullseye—and sometimes even sailors standing behind the shooter—frees up space on the amidships.