Because of the artillery shortage, some artillery units were armed as infantry. General Freyberg wrote about the situation. There seem to have bee, one hundred guns sent to Crete. Fewer than that arrived at Crete. Others arrived without essential items, such as sights, ammunition, some ammunition without fuses. The gunners were a variety of men There were regular British army, Australians or men from New Zealand. There were many clever men. In one case, a man made a sight from wood and chewing gum. Other men made charts that let them "shoot without sights or instruments." There were no complaints and everyone got involved. Of the Italian guns, some were 75mm and others were 100mm. Of the rifles and machine guns, there were American, Italian, and British.
While all this was being done, the soldiers were constantly attacked from the air. That included ships in Suda Bay, which had started prior to the Greek withdrawal. The unloading of ships was so dangerous, that they started using volunteers. They only stopped when the ship being unloaded was being attacked. In one case, a partially sunk ship had Bren carriers on deck that were unloaded.
This is based on the account in "Greece, Crete, and Syria" by Gavin Long.