On 18 April 1672 Wrenn was appointed commander of the Hopewell fireship, and in the following year of the Rose dogger.
[2] He sailed from Plymouth on 26 December, and after a most favourable passage arrived at Barbados on 16 January 1691 – 1692, when his force consisted of the Mary and, besides the Norwich, five fourth-rates, ships of from forty to fifty guns.
He had orders to send one of these with the trade to Jamaica; but, receiving intelligence that the French were in greater force than had been supposed, he detached two on this duty.
Not meeting with the enemy in a cruise of five days, he returned to Barbados, and, apprehending that the whole French fleet had gone to Jamaica, he sailed again on 17 February.
On 21 February off Desirade, he sighted the French fleet of more than three times his strength—eighteen ships of from forty to sixty guns, with some six or seven fireships and tenders.