He was midshipman of the Roebuck on 9 October 1776, when her first lieutenant was killed in action with the batteries at the mouth of North River and was promoted to the vacancy caused by his death.
Aplin's further promotion was rapid, and on 23 November 1780 he was appointed captain of the Fowey, a frigate of 24 guns.
He was still in her at Yorktown in the following October, when she was destroyed by the enemy's red-hot shot; after which he served, with his crew, on shore under the orders of Lord Cornwallis.
He had no further service at sea until, in 1797, he was appointed to the Hector of 74 guns, which, after the Battle of Cape St Vincent reinforced the fleet off Cádiz.
[1] In 1802 the British East India Company named a vessel for him, the Admiral Aplin; unfortunately a French privateer captured her in 1804 near Mauritius.