Like many other senior officers involved in the Papuan campaign, he was then transferred to a less important posting by General Sir Thomas Blamey.

Posted to the 1st Field Artillery Brigade,[11] he landed at Gallipoli on 25 April 1915, serving as a forward observation officer and directing naval gunfire against Turkish positions.

[11][15] He returned to Australia in April 1919, by which time the war was over due to the armistice of 11 November 1918, and left the AIF in late June.

[11] When the Second World War began, Clowes was made a temporary brigadier in the AIF, and in April 1940 was appointed commander of the Royal Australian Artillery, I Corps.

Clowes was successful in holding the gorge against a strong German tank attack, until the situation on other parts of the front stabilised.

[16] Although Greece fell and the campaign was a failure, Clowes' tactics minimised casualties in the withdrawal of the allied force.

[11] In May 1942 General Douglas MacArthur, Allied Commander in Chief of the South West Pacific Area (C in C SWPA), ordered the construction of an airfield at Milne Bay, at the eastern tip of New Guinea.

Once buildup was complete, the garrison assumed the name Milne Force, and Clowes, now promoted to Major General, was given command.

[25] Milne Bay is a very high rainfall area, and the all-pervading mud made transport a constant problem for Clowes.

Several times during the battle, urgent signals arrived from MacArthur and Blamey, warning of imminent Japanese reinforcements, and urging him to pursue and exterminate the enemy landing force immediately.

[28] Rowell refused to relay this to Clowes, and instead wrote "Confident you have the situation well in hand and will administer stern punishment".

[30] MacArthur and Thomas Blamey determined that rather than being commended and rewarded for the victory, Clowes should be relieved of his command and sidelined for the duration of the war, for showing insufficient "vigour".

[31][32] Blamey wrote to Sydney Rowell, now Clowes' superior officer in Port Moresby: My Dear General, I would like to congratulate you on the complete success of operations at Milne Bay … but it appeared to us here as though by not acting with great speed Clowes was liable to have missed the opportunity of dealing completely with the enemy and thus laying himself open to destruction if after securing a footing, the enemy was able to reinforce their first landing party strongly".

[12] His chief staff officer at Milne Bay, Colonel Fred Chilton, said he was … a fine commander and a steady man.