Maatschappij voor Scheeps- en Werktuigbouw Fijenoord built Maasdam as yard number 289, launching her on 21 October 1920 and completing her on 6 August 1921.

Maasdam was part of a new generation of NASM ships, nearly all of which had steam turbines, which were reduction-geared for economy.

Maasdam had a three Brown-Curtis turbines, made by John Brown & Company in Clydebank, Scotland.

Koninklijke Maatschappij 'De Schelde' Scheepswerf en Machinefabriek in Vlissingen launched Edam in January 1921.

Outward voyages called at Antwerp, Boulogne, Bilbao, Santander, Gijón, A Coruña, Vigo, Havana and Vera Cruz.

[7] On 30 November 1926 Maasdam was about 400 nautical miles (740 km) off the coast of Spain,[8] en route from Vera Cruz to Rotterdam, when she signalled that she was on fire.

[1] By 1934 her navigation equipment included wireless direction finding,[11] and the call sign PFQS had replaced her code letters.

[12] On the evening 17 February 1940, U-48 sank the Finnish cargo ship Wilja in the Western Approaches at position 49°24′N 07°11′W / 49.400°N 7.183°W / 49.400; -7.183.

She returned carrying general cargo via Halifax, Nova Scotia, where she joined eastbound Convoy HX 60.

[15] On 12 December she collided with the British steamship Anthea off the coast of Canada, sinking her at position 44°48′N 46°37′W / 44.800°N 46.617°W / 44.800; -46.617.

When a shovel was not to hand, one crewman used his overcoat to pick up a thermite bomb, which burned his arms and temporarily damaged his eyes.

[12] She also embarked 32 passengers, including 11 US Marines on their way to serve at the Embassy of the United States, London, 17 American Red Cross nurses on their way to work at the ARC-Harvard Hospital[18] at Salisbury in Wiltshire.

President Franklin D. Roosevelt had authorised an exemption from the Neutrality Act of 1939 to allow the nurses and marines to travel on the ship of a belligerent nation.

[12] On 21 June, Convoy BHX 133 from Bermuda joined HX 133 at sea,[17] increasing its size to 58 merchant ships.

[22][23] Shortly after 2100 hrs that evening, a third U-boat sank the British steamship Brockley Hill.

But in the early hours of 27 June, U-564 attacked the convoy about 300 nautical miles (560 km) southwest of Iceland,[21] at position 59°56′N 30°35′W / 59.933°N 30.583°W / 59.933; -30.583.

She immediately exploded, killing 43 of her 49 crew,[26] and showering Maasdam with débris, injuring a number of people, including the Master, Captain Boshoff, and his Third Officer.

Maasdam's wheelhouse and chart room were destroyed, and her bow soon sank to sea level.

[29] Captain Boshoff ensured that Maasdam's wireless telegraphy codebooks had been thrown overboard in their weighted bag.

Boat 5 reached the Norwegian tanker Havprins, which was the third ship in the eighth column, behind Maasdam and Kongsgaard.

[30] Havprins' crew had thrown a lifeline into the water, with an empty drum secured to the end for flotation.

They included Maasdam's Chief Engineer, Pieter Schutter, who found one of the nurses, Maxine Loomis, clinging to the drum "in utter terror", apparently in shock.

[31] Randa detached from HX 133 and landed its share of Maasdam's survivors in Reykjavík,[32] where another NASM ship, the liner Volendam, later picked them up.