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The Mark 90 nuclear bomb, given the nickname "Betty", was a Cold War nuclear depth charge, developed by the United States in 1952.

It had a length of 10 ft 2 in (3.10 m), a diameter of 2 ft 7.5 in (0.80 m), and a weight of 1,243 lb (564 kg), and it carried a Mark 7 nuclear warhead with a yield of 32 kilotons. Its purpose was to serve as an anti-submarine weapon for the United States Navy.

A test of the Mark 90 was conducted in 1955, as Operation Wigwam.

A total of about 225 such bombs were produced.^[1]

All units were withdrawn from service by 1960.

On September 25, 1959, a United States Navy Martin P5M-2 Marlin (BuNo 135540, SG tailcode, '6', of VP-50) was patrolling out of NAS Whidbey Island when it was forced to ditch in the Pacific Ocean, about 100 miles (160 km) west of the Washington-Oregon border.

A Mark 90 depth charge casing was lost and never recovered, but it was not fitted with an active warhead.^{[citation needed]} The ten crew members were rescued by the US Coast Guard, after ten hours in a raft. The press was not notified at the time.^[2]

• List of accidents and incidents involving military aircraft (1955–1959)

• Official Defense Department film on 1955 underwater test of Mark 90 nuclear depth charge