More about bombing attacks on Tobruk in 1941

Apparently, the effectiveness of anti-aircraft barrages across the line of flight greatly effected daylight high level bombing attacks. After July 1941, bombing attacks mostly switched to the night. They still might attack during the day if there were inviting targets, but mostly, they found that they could more effectively bomb at night. There is another table giving the numbers of night bombers employed per month in 1941.

                                              Night Bombers employed
Last 21 nights of April          32
May                                       74
June                                     132
July                                      126
August                                 205
September                           187
First 9 days of October       152

The night raids in April and May 1941 were mostly low-level attacks to drop "thermos" bombs. By June, all night raids but one were made with high-level bombing. A major change started with 21 July, when night bombers dropped mines hoping to block the harbor entrance. Two more mine laying attacks occurred in the last week ofo July. The night bombing intensified, and this became a serious matter. Some raids were as large as fifty aircraft at night. The enemy also mixed bombing and minelaying to attempt to confuse the defense. Attacks did not occur every night, but were mostly during nights with moon light. Up through July, night bombers would attack singly. As many as 30 to 50 per cent were turned back by barrages. Anti-aircraft gunners were hard pressed by lack of sleep. To counter aircraft dropping mines, listening devices were used and they fired a barrage in conjunction with searchlights center and ends of the harbor. The barrage, when it could be fired in time, was so effective that the enemy would avoid it.
To understand the effort involved, from 10 April to 9 October 1941, some 3,525 aircarft were fired on by anti-aircraft guns. They lost 40 gunners killed and 128 men were wounded. They fired greater than 49,000 rounds of 3.7in anti-aircraft rounds. The available guns can be seen by the rounds fired. Another 3,700 40mm rounds were fired. The scale of 20mm guns meant that they fired some 75,000 rounds. There were also captured Italian guns in use, so there were even more than these fired. The guns were thought to have definitely destroyed 74 aircraft. Another 59 aircraft were probably destroyed. finally, another 145 aircraft were thought to have been damaged. This is based on the account in Vol.III of the Australian Official History.