Tobruk shelliing from September 1941 onwards

Conditions changed at Tobruk after the heavy air raid on 1 September 1941. The pressure from the air continued, but the main problem was shelling from artillery. The ammunition shortage continued, so that British manufactured guns were only allowed to fire ten rounds a day. The next major development saw the ammuntion depot with Italian ammunition was bombed and destroyed. That meant that Italian 75mm and 100mm guns fell under the same restrictions. During August, a great deal of ammunition arrived by sea. Most of the ammunition went to the front line units, so only 100 rounds were added to the ammunition reserve. At the end of August, there were 101,993 rounds at Tobruk.
Starting in September, the procedure for counter-battery fire changed. The guns would fire one-after-another, but timed with stopwatches so that all the rounds would hit the target simultaneously. The guns that fired on the Tobruk harbor were troublesome-enough that there were planned artillery attacks where the number of rounds restriction was ignored so that they could counteract the "harbor guns".
For example, a storeship that had been converted from a trawler, was to arrive in the Tobruk harbor at 4:30am. The ship was late, however, and arrived after dawn. The guns attacking the harbor were effective and slowed the unloading process. The 104th RHA had two troops return fire wqith 353 rounds. Enemy counter-battery fire was effective and hit one of the two troops, "killing one man and wounding two others." On 4 September, there was a meeting where the issue was discussed. The new plan was when the enemy was firing on the harbor, to ask the navy how much problem was caused. If the firing was very troublesome, they would do counter-battery firing and bring in other guns to hit the "enemy counter-battery guns".
On 6 September, the enemy fired on the port and hit a jetty used for destroyers. They also hit the 104th RHA troop that they had hit previously and on a troop of 60-pounder guns from the 2/12th Regiment. The new plan went into effect and some 350 25pdr rounds and 77 60-pounder rounds. Afterwards, they observed an ambulance leaving the enemy position. The Tobruk guns had not taken any casualties, showing the effectiveness of the new plan. On 7 September, both sides had another go at the artillery battle. The RAF hit the enemy gun positions. When one gun still fired on the harbor, The 25pdrs and 60pdrs responded with counter-battery fire. The enemy gun and the 60pdrs fired at each other. The 60pdrs fired the last rounds, so they won the impromptu duel. This is based on the account in Vol.III of the Australian Official History.