LONDON (AP) — U.K. Defense Secretary Ben Wallace formally submitted his resignation on Thursday amid speculation that Prime Minister Rishi Sunak will name his successor later in the day.

Wallace, who said last month he would resign before the next Cabinet reshuffle, ended four years in the post in which he oversaw the military response to the war in Ukraine.

He used his resignation letter to press for increased funding for the military, long his primary issue.

“I genuinely believe that over the next decade the world will get more insecure and more unstable,’’ Wallace wrote in his letter to Sunak. “We both share the belief that now is the time to invest. Ever since I joined the Army I have dedicated myself to serving my country. That dedication, however, comes at a personal toll to me and my family."