Upon his return to the American colonies, Collier provided support for General William Howe's landing at Long Island, New York on 22 August 1776. Sent to Halifax, Nova Scotia as a senior officer by Admiral Richard Howe, 1st Earl Howe, Collier would capture the American frigate USS Hancock after a long chase on 8 July 1777. Collier followed up on his success the following month by destroying supplies at Machias, Maine, thereby ruining American plans for an invasion of Nova Scotia.
One amusing anecdote of the Rainbow was written by Capt Alexander McDonald paymaster of the Royal Highland Emigrants Regiment, 20 Dec 1778:"...Flanking Companies. I am told they are a terror to All the Soldiers & Sailors about Halifax a few nights ago a boats Crew from the Rainbow was ashore & Comitting some disorders & Riots in One of the Houses w'ch the Grenadiers frequent a party of them came in immediately beat the Sailors damnably and each of them took one upon his back threw them into their boat like so many bags of wool lanched the boat & set them adrift."
Succeeding Admiral James Gambier as commodore and acting commander-in-chief of the North American station on 4 April 1779, Collier led a highly successful raid with General Edward Mathew on the Virginia coast on 29 May.
The following day, on 30 May, Collier joined the British assault on Stony Point, New York providing support for Sir Henry Clinton, managing to sink an American rebel ship carrying loot and supplies captured from the fort. One of the few naval commanders able to get along with Clinton, Collier also provided naval support for Clinton's raid into Connecticut in June before returning to New York in late-August. During this time he descisively defeated the largest rebel naval force of the war, inflicting what was the United States' worst defeat at sea until Pearl Harbour.