The bullet, which is being auctioned by a UK-based seller, is said to be an unfired cartridge from The Aud, which to this day remains sunk off the coast of Co Cork.

The opening bid for the bullet is �500, but no bids have been registered yet, possibly because bidding won't close until 26 March.

The Audwas commissioned by Roger Casement and other volunteers to import arms to Ireland for use during the 1916 Rising.

The ship carried an estimated 20,000 rifles, 100,000 rounds of ammunition and 10 machine guns.

However, it was intercepted by the British navy off the coast of Cork on 20 April 1916 and blown up by the ship's commander Karl Spindler.

According to the seller, the bullet being auctioned was "raised from the remains of No 2 hold on the wreck of The Aud by divers on the 90th anniversary of the sinking in 2006".

A first edition of Captain Spindler's book, The Mystery of the Casement Ship, published in 1931, is being auctioned by the same seller. Apparently signed by the captain, the starting bid is �300.

A poster of the ship's plans is also being auctioned at a starting price of �99.99. "This would be ideal for a pub, club or museum, " the seller said.

No interest has yet been registered on either of these items.