Air attacks on Tobruk and the anti-aircraft defenses

Brigadier Slater commanded the 5th Anti-Aircraft Brigade at Tobruk during the siege. The harbor and base were priorities for anti-aircraft defense. This was a constant struggle as the enemy continued to evolve their operations. The units involved were typically below strength and guns were in constant need of repair. That meant that they needed spare parts for the guns, as well as spare guns. They also relied on laborers to help with digging and the like. The enemy targeted guns, so that they would repair.
Early in the siege, the enemy staged daylight air attacks, often with dive bombers. As the defense capabilities improved against dive bombers, the enemy switched more to night bombing attacks. The air attacks were constant, with only one day during the 9th Australian Division's time at Tobruk when there were no air raids. All these dates are from 1941.

                      Dive bombing      Total                 Night Raids  Total Bombing  Day Reconnaissance
                                                Daylight raids                             Raids
April 10-30      21                       41                       11                   73                      27
May                 17                       60                       22                   99                      58
June                  6                        58                       76                 140                      39
July                   4                       91                        43                 138                     46
August             11                      55                        77                  143                    30

The defenders took a while and had to experiment to find tactics to deal with dive bombers. The enemy made a first heavy dive bombing attack on 14 April 1941. The guns fired a fixed barrage to explode at 3,000 feet. They found that some aircraft had gotten in before the barrage was fired. to counter that danger, they set up an observation post on the escarpment where they could look down on the harbor. There were problems found with inadequate depth to the barrage. The guns often fired too soon in the attack. The barrage had to spread from 3,000 to 6,000 feet and was fired to swing across the harbor area. They had four Italian 102mm anti-aircraft guns which were repaired and employed. By August, they had found three more of the Italian guns and added them to the defense. The static 40mm guns were used to engage aircraft that survived the barrage. The 12 40mm static guns were manned by the 40th Light Anti-Aircraft Battery.
The defenses added three 20-barrel parachute rocket launchers provided by the navy. The rockets had parachutes and trailed long wires. Small bombs were attached to the end of the wires. They were first used on 18 August against a dive bombing attack. They successfully disrupted the attack.
The enemy resorted to attacking the anti-aircraft gun positions. They damaged six guns that were all repaired. The gunners quickly learned that they were safest by staying in action and shooting at the attacking aircraft. That was a lesson learned in May and June 1941. Dive bombers were used against the guns. They started on 10 April and ended on 1 September 1941. This is based on the account in Vol.III of the Australian Official History.