The relative peace along the eastern enclave was short lived and during the night of 15 June German reconnaissance patrols reported that 8th Army's advanced guards had crossed the frontier wire and were driving across the desert towards the Via Balbia. In Rommel's eyes this was the big attack and it had been expected for Luftwaffe reconnaissance had told of the forming up of strong armoured and lorried columns behind the British front. Intelligence appreciations indicated that 8th Army's advance was being made in three columns. The right wing would move against the garrisons in the Halfaya Pass from the east, the central column would move against Capuzzo and go on to attack Sollum, while the third column, undertaking a march across the desert, obviously had the intention of cutting off, surrounding, and then destroying the Axis forces south of Bardia.
Rommel moved 5th Light Division to a point south of Tobruk there to act as a mobile reserve and sent orders to 15th Panzer Division, in position around Gambut, to prepare to move eastwards. His simple battle order read 'Halfaya will be held and the enemy beaten'. To support the assault Ariete was ordered forward but reported that its Santa Maria detachment, having neither fuel nor rations, could not undertake the mission. Until the direction of the main British thrust became clear 15th Panzer was held in position to await developments. The whole eastern flank was embattled; Capuzzo fell to a massed tank attack; at Sidi Omar the outnumbered garrison was fighting for its survival; but at Halfaya all the British assaults had been repulsed and the German battalion then won back the ruins of Fort Capuzzo. Another wave of heavy British tanks swept up to the fort and rolled over the defenders. Capuzzo was lost again.
Rommel unleashed his panzer division and it roared across the desert towards Capuzzo. In the afternoon of 15 June the armoured forces of both sides clashed and the 8.8cm gun proved itself as a first-class tank killer. A single battery of three guns in line held position with some 8th Panzer Regiment vehicles and took under fire a wave of Matilda tanks as they rumbled forward. Eighteen of them were destroyed. By sunset the outcome of the battle was still unclear and conflicting reports were reaching the headquarters of 8th Army and of Africa Corps. But one thing was clear; the speed of the panzer reaction had held Wavell back from reaching his objective and he had lost, according to German reports, more than 60 tanks.
At first light on 16 June the panzer division renewed its attack against Capuzzo. On the British side the armoured might of 7th Armoured Division had been concentrated into a giant steel fist and was striking westwards. The two forces met in a head-on collision and the impetus of the British assault forced 15th Panzer Division to give ground. It lost heavily in the battle and was soon reduced to a strength of only 35 vehicles. The 5th Light Division was ordered forward and came into action against the British flank by striking out of Sidi Omar. This was a day of crisis for both sides and there hung over the battlefield the unresolved question — would Halfaya Pass be captured? If Wavell's forces could seize the pass then they could reinforce the battle with fresh supplies of men and armour. Against this flood of material the whole eastern enclave would be able to offer no long resistance and the Axis armies, weakened in the battles around Halfaya and Capuzzo, would be crushed against the rock of Tobruk. .
The fate of the German and Italian enterprise in Africa depended, for a short time, upon the ability of a heavily outnumbered German garrison to hold its ground. The first attack came in and the British and Indian troops were driven back. A drum-fire of shells was poured upon the defenders and then, during the afternoon, covered by another barrage the second assault came in, was repulsed, came in again and again, and was flung back again and again. Not only did the German battalion hold its positions but counterattacked whenever possible.
In the south, at Sidi Suleiman, 5th Light and 15th Panzer Divisions were ordered to smash forward in a combined attack against the flanks and rear of Wavell's Army but 5th Light struck heavy opposition and only weak elements were able to struggle forward to reach the Sidi Omar area. The main of the division was caught by the British artillery and dispersed. The 15th Panzer stood waiting for the arrival of its sister division.
At midnight on 16 June a simple battle order was given to both divisions - 'Advance upon the Halfaya Pass and destroy the enemy there', and after first light the panzer boxes moved out to battle with an enemy against whom the tide of fortune had turned. The delay in capturing Halfaya Pass was having a serious effect upon the British conduct of operations and on the Egyptian side of the pass still lay the convoys ready to rush forward the reinforcements which Wavell and his depleted armour needed to maintain the tempo of the attack. The 7th Armoured Division had suffered crippling losses and its tanks were running short of ammunition. Wavell was faced with a crisis but this intelligence was not known to the German commanders and Rommel, concerned at his own weakness in the Halfaya area, demanded that divisions in position around Tobruk be sent to support the Bardia garrison and to strengthen the Sollum front. The Libyan High Command released Pavia Division and sent it forward.
Then a wireless intercept picked up messages from 7th Armoured and from these Africa Corps knew that a striking victory lay within its grasp. Revivified, the combined panzer power of 5th Light and 15th Divisions struck at Wavell’s force intent upon the killing blow. So impatient were the soldiers of the Africa Corps to join battle that ahead of the panzers drove the gun line of 8.8cm weapons to take the British under fire at close range and by a storm of gun fire to force Wavell’s tanks back eastwards in headlong flight. The first thrust cost 7th Armoured Division a further 14 of its armoured fighting vehicles, but the British were not beaten and put up such resistance to the assaults of 5th Light Division at Sidi Suleiman that their defence could only be beaten down with Stuka dive-bombing.
Other wireless messages were intercepted at 11:00 hrs reporting that the 7th Armoured Division's tanks had fired off all their ammunition. They would be forced to withdraw. During the afternoon of the 17th the German columns met and joined forces in an approach march upon Halfaya where they linked with the garrison which, having been supplied by air-drop, was still busily engaged in beating off the attacks of 4th Indian Division. The 15th Panzer Division then moved forward with the still aggressive Halfaya garrison in a final counter-attack which brought the main fighting to a close. Only a sweep and search operation needed to be undertaken in the Sollum, Capuzzo, Sidi Omar, and Bardia sectors to round up the scattered survivors of the British divisions.
The great three-day Sollum tank battle was at an end and like all the battles in the desert it had been a melee having no properly defined front lines or rear areas, but had been a confusion of noise and destruction. It had, however, been the mightiest armoured engagement to date in the African theatre of operations. More than 200 British tanks were left behind on the battlefield and 7th Armoured Division went back across the wire with only 24 runners. The 15th Panzer Division lost 15 of its tanks and 5th Light had 10 of its vehicles destroyed. But strength returns for Africa Corps on 20 June reported the figure of 136 vehicles. The recovery and repair sections had once again shown their ability.
The losses in men from the start of the campaign to 5 June were reported by Africa Corps to be 513 killed in action, 1689 wounded, and 1015 missing. During the period from 15 to 20 June the numbers lost, including the figures for the Tobruk front, were 95 dead, 355 wounded, and 235 missing.