The helmet was discovered in a Wisconsin house in February this year – apparently it had been bought back in the 1950w as an ‘item of curiosity'.
The helmet bears the serial number #2198, which shows it is an extremely early model made in the inaugural year of the Mark V – 1916. In a US Navy manual from 1916, there is a photograph of a Mark V helmet with the serial number #2178, so this helmet is only 20 ahead.
Don Creekmore, the owner of The Nation's Attic, which is handling the sale through its Vintage Scuba Auction, said: “This truly is a unique opportunity to own arguably the most-important US Navy diving helmet made in the 20th century.”
The helmet is a no-reserve auction, with the highest bid currently at $16,000. You can bid on the helmet at the auction site.