Bold (decoy)

It consisted of a metal canister about 10 cm (3.9 in) in diameter filled with calcium hydride.

It was launched by an ejector system colloquially referred to as Pillenwerfer (English: "pill thrower").

When mixed with seawater, the calcium hydride produced large quantities of hydrogen, which bubbled out of the container, creating a false sonar target.

A valve opened and closed, holding the device at a depth of about 30 m (98 ft).

[1] The Royal Navy called it SBT (Submarine Bubble Target).