The scale of air attacks on Tobruk were increasing and this prompted General Morshead to send a message to the Western Desert Force headquarters. The danger was that the scale of air attacks would make it difficult to use the harbor at Tobruk. Another issue was that the recent losses in aircraft based at Tobruk were not being replaced. Three aircraft had been lost on 23 April 1941, and this already had created a problem. The RAF reacted by deciding to withdraw the remaining two Hurricane fighters on 25 April. That would leave the two Lysander army cooperation aircraft without fighter protection. Tobruk relied on the Lysanders to spot for artillery.
We find that for all of the Western Desert Force, the RAF had only 13 Hurricanes and they could not afford to leave them in Tobruk, as they would likely be lost. The only benefit to Tobruk was that one flight of reconnaissance Hurricanes would continue to support Tobruk.
A sandstorm shut down operations at Tobruk on 26 April. The engineers kept working during the sandstorm to lay more mines, particularly ones that would fire on contact ("hair trigger"). Other engineers worked on the inner defensive minefield behind the Medauuar feature.
The sandstorm died down on 27 April, which allowed the Germans to stage an attack on the heavy anti-aircraft guns with 24 dive bombers. They shot down one dive bomber, but four guns were temporarily disabled. The gun crews took losses, as well. The anti-aircraft commander, Brigadier Slater gathered information about the attack. He found that the initial attack was made by Ju-88's with a fighter escort. They got fire from the heavy anti-aircraft guns. They thought that the next stage was a dive bomber attack on the heavy anti-aircraft guns. Probably many more than fifty dive bombers attacked in groups of at least 12 planes. In some cases, they came out of the sun, so they were not seen before they struck. Two guns sites had guns in a "porcupine formation". These two sites took less damage and the guns were kept in action during the attacks. Two other sites fared worse. At one of the two sites, they had not even seen the dive bombers before they were hit. What they found was that the best thing to do was for the gun crews to continue to fight during the attacks and not dive for cover. We can see the situation by realizing that in the final 20 days of April 1941, Tobruk was attacked by 386 dive bombers during 21 incidents. The anti-aircraft gunners kept their nerve and fought their guns with success. This is based on the account in Vol.III of the Australian Official History.