ZK-ZZ Lighter-Than-Air Aircraft.
ZK KITE BALLOONS.
ZM BARRAGE BALLOONS.
ZMQ MARINE BARRAGE BALLOON SQUADRONS.
ZN NONRIGID AIRSHIPS.
ZR RIGID AIRSHIPS.
ZR1 Shenandoah (stricken)
ZR3 Los Angeles (stricken)
ZR4 Akron (stricken)
ZRS5 Macon (stricken)
ZRMC2
ZZ LIGHTER-THAN-AIR AIRCRAFT.