After the armistice, Swallow was transferred to the Mediterranean fleet and served in the Black Sea covering the evacuation of demobilised forces from Batumi and Marmara Ereğlisi.

Three Yarrow boilers fed steam to two sets of Brown-Curtis geared steam turbines rated at 27,000 shaft horsepower (20,000 kW) and driving two shafts, giving a design speed of 36 knots (67 km/h; 41 mph) at normal loading and 32.5 knots (60.2 km/h; 37.4 mph) at deep load.

The vessel normally carried 301 long tons (306 t) of fuel oil, giving a design range of 2,750 nautical miles (5,090 km; 3,160 mi) at 15 knots (28 km/h; 17 mph).

[4] The ship was designed to mount two 18-inch (457 mm) tubes either side of the superstructure but this addition required the forecastle plating to be cut away, making the vessel very wet so they were removed.

[9] Shortly after entering service, on 1 October, the ship took part in a flotilla led by the destroyer leader Montrose that sailed to intercept retreating German forces, but did not find any.

[10] After the armistice, Swallow was recommissioned on 17 February 1919 into the Sixth Destroyer Flotilla as part of the new Mediterranean fleet.

[11] The ship then transversed the Bosporus into the Black Sea to Batumi, staying until 9 July to cover the evacuation of troops to Russia.