As initially constructed, the yacht had a gross register tonnage (GRT) of 848 and was powered by a triple expansion steam engine driving two shafts.

The vessel had a maximum speed of 12 knots (22 km/h; 14 mph) and was armed with one 4-inch (102 mm) naval gun, an ASDIC set and depth charges.

[1][2][4] Owned initially by Albert C. Burrage, the vessel was leased by the United States Navy during the First World War.

[5] The yacht was overhauled and upon completion, was assigned to the 1st Naval District based at Boston, Massachusetts and designated the flagship.

Aztec's duties comprised naval facilities inspections and escorting submarines from Boston to New London, Connecticut, and troopships to Halifax, Nova Scotia.

[5] After failing to acquire any British vessels at the outset of the Second World War for auxiliary purposes, the Royal Canadian Navy discreetly searched the American market for suitable ships.

[5] Initially carrying the pennant number S10 and later Z10, she was commissioned as Beaver into the Royal Canadian Navy on 4 April 1941 at Halifax, Nova Scotia.