She was the third of four Blue Funnel Line ships to be named after Agamemnon, the king of Mycenae during the Trojan War.

Between 1929 and 1931 Blue Funnel Line had a class of five cargo ships built to the same design by four different UK shipyards.

[1] Caledon Shipbuilding & Engineering Company built Menestheus in Dundee, launching her in August 1929 and completing her that September.

[4] Scotts Shipbuilding and Engineering Company built Ajax at Greenock, launching her in December 1930 and completing her in April 1931.

[12] On 18 October 1940 she joined the 1st Minelaying Squadron at Kyle of Lochalsh (port ZA), along with four other auxiliary minesweepers, including her sister ship Menestheus, plus an escort of Royal Navy destroyers.

In February 1941 Menestheus was damaged by a drifting British mine, and Agamemnon towed her back to Kyle of Lochalsh.

The 1st Minelaying Squadron completed laying the Northern Barrage in late September 1943, and that was disbanded that October.

[11] Conversion included installation of a cinema and canteen, to be staffed by mercantile crews of the Royal Fleet Auxiliary.