During the Second Anglo-Dutch War Tjerk was appointed full captain on 27 March 1665. He commanded "d' Elff Steden" in the Battle of Lowestoft, managing with great personal courage to free his ship from an entanglement with several other burning Dutch vessels, set alight by an English fireship. This fight was a severe defeat for the Dutch and those who by their bravery set a contrast to the general incompetence shown during the battle, were hailed as heroes by the populace. Tjerk in a written report severely criticised his fallen supreme commander Van Obdam. The Frisian admiralty board, in need to replace the also killed Lieutenant-Admiral of the Frisian fleet, Auke Stellingwerf, and sensing the public mood, appointed Tjerk Lieutenant-Admiral of Frisia on 29 June 1665. He thus jumped two ranks, not an uncommon occurrence for the Dutch navy in that century.