By April 1944 Grimshaw was commanding officer of the 1st Battalion of the 1st Punjab Regiment. On 18 April 1944 he was one of the first soldiers to enter Kohima Garrison breaking the siege during the Battle of Kohima. He was mentioned in dispatches for a second time during the Burma Campaign. In March 1945 he was promoted to brigadier and took command of the 161st Indian Infantry Brigade, holding the position for a year. In June 1945 he was awarded the Distinguished Service Order for services in Burma.