Its back the dreaded single letter.

H -- Hall-Aluminum Aircraft Corporation, now Consolidated-Vultee Aircraft Corporation

H -- Heavier-than-air rotary wing aircraft, helicopter

H -- Heavy or 4-engine plane

H -- Hospital plane suffix to plane designation, as PBJ-2H

H -- Howard Aircraft Corporation

H -- Medical Department aboard a carrier

H -- Mustard gas

H -- Stearman-Hammond Aircraft Corporation

Well, now when we look at this list we see that mustard gas has been outlawed for many years. Stearman-Hammond has not made a military aircraft in years. Howard aircraft corp is no longer around and more than likely never been heard of by many of us. Heck, most of the aircraft companies in these lists are no longer around.

H is still used for medical spaces onboard ships.