Schrader 5 Bolt/USN Mark II Helmets in History Challenge Coin (Series Set # 3)

The third in a series of limited production collectible “Helmets in History” challenge coins produced for and sold by the Historical Diving Society USA. Each coin in the series will highlight a diving helmet with a positive impact on deep sea diving.

Every coin produced has the original HDS logo of an Augustus Siebe helmet on one side and the featured “Helmets in History” helmet on the reverse. This coin features the U.S. Navy Mark II helmet.

These collectible coins are 1.75 in diameter, are highly detailed, and will be a prized possession for years to come. Each comes in a soft PVC envelope.

Introduction of the famous MK V helmet made it necessary to designate different styles of earlier helmets. From the U.S. Navy's 1916 Diving Manual; MK II - Bolt Type; wide breast plate; screw faceplate; round top and side windows; "Schrader" type regulating escape valve; safety valve and air inlet connection; manufactured by A. Schrader's Son (Inc.), Brooklyn, N. Y.

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