The '1^st Battle of Tobruk' was fought between British-led and Italian forces for the port of Tobruk on the Mediterranean coast of Cyrenaica in Italian Libya as part of 'Compass' (i) (6/22 January 1941).

After defeating the Italians in the 'Battle of Bardia' (3/5 January 1941), Major General Iven Mackay’s Australian 6^th Division and Major General Michael O’Moore Creagh’s British 7^th Armoured Division pressed to the west and made contact with the Italian garrison of Tobruk on 6 January. The Italians had fortified Tobruk, their only naval base in eastern Cyrenaica, before the outbreak of World War II, but after being routed at the 'Attack on Nibeiwa', the 'Battle of Sidi Barrani' and the 'Battle of Bardia', the Italian 10a Armata had lost eight of its nine divisions and had only the 61a Divisione fanteria 'Sirte' and groups of stragglers with which to defend the port.

In September 1940 the Italian 'Operazione 'E'' invasion of Egypt had begun but was quickly brought to a halt after 62 miles (100 km) at Sidi Barrani, where the Italians dug in. At first the British prepared to resist a renewed Italian advance to Mersa Matruh, but when this did not occur a raid by the Western Desert Force, with the possibility of exploiting any success, was planned on the Italian positions around Sidi Barrani. This 'Compass' (i) raid began on 9 December 1940 with the surprise 'Attack on Nibeiwa', where General di Divisione Pietro Maletti’s brigade-sized Ragruppamento 'Maletti', the only Italian armoured unit in Egypt, was annihilated. On 10 December Major General Richard O’Connor’s Western Desert Force engaged the three divisions of the Gruppo divisioni libiche and the 64a Divisione fanteria 'Catanzaro' at the 'Battle of Sidi Barrani' and defeated them by 11 December.

With the 63a Divisione fanteria 'Cirene', the last Italian division on Egyptian soil, retreating towards Libya, the 7^th Armoured Division pressed on and by 15 December had cut the road linking Bardia and Tobruk. At Bardia the Italians had concentrated Generale di Corpo d’Armata Annibale Bergonzoli’s XXIII Corpo d’Armata, comprising the 1a CCNN Divisione '23 Marzo', 2a CCNN Divisione '28 Ottobre', 62a Divisione fanteria 'Marmarica' and 63a Divisione fanteria 'Cirene'. Other elements were four light tank battalions, the remnants of the 64a Divisione fanteria, and the XXI Corpo Reggimento artiglieri. After careful preparation the British attacked and defeated the Italian defenders between 3 and 5 January 1941.

On the morning of 5 January, while Australian forces were still mopping up the southern cauldron at Bardia, General Sir Archibald Wavell, the commander-in-chief of the British Middle East command, ordered the 7^th Armoured Brigade of Creagh’s 7^th Armoured Division to advance to the west, bypass Tobruk and thereby isolate it. By 6 January the brigade had reached El Adem, and by 7 January the bulk of the British forces had arrived and cut off Tobruk. The Australian 19^th Brigade group placed itself opposite the eastern defences of Tobruk and the Australian 16^th Brigade group took over on the western side. The 4^th Armoured Brigade moved to the west of the city, the 7^th Support Group blocked the western exits and the 7^th Armoured Brigade screened the force from interference from the west.

Graziani informed Benito Mussolini, the Italian dictator, that the 34-mile (54-km) Tobruk perimeter was held by only 22,000 men with 340 pieces of artillery, numbers wholly inadequate for the task. On 9 January, Graziani informed the garrison commander, Generale di Divisione Enrico Pitassi Mannella, that there would be no attempt at relief. Graziani ordered Generale di Corpo d’Armata Giuseppe Tellera, commander of the 10a Armata, to fall back with the 60a Divisione fanteria 'Sabratha', his last division, to a line between Derna and Berta, while directing Generale di Brigata Valentino Babini’s Raggruppamento 'Babini' to Mechili. After being informed by Graziani that he was on his own, Pitassi Mannella ordered the destruction of the bridge at Sidi Daud on the Bardia road and the bridge at Wadi es Sahel on the Derna road.

Under the command of Pitassi Manella’s XXII Corpo d’Armata, the garrison of Tobruk was based on Generale di Divisione Vincenzo della Mura’s 61^st Divisione fanteria 'Sirte' with six battalions of infantry in two regiments, one artillery regiment with 75- and 100-mm (2.95- and 3.94-in) guns, single machine gun, mixed engineer and replacement battalions, one tank regiment with single medium tank and tankette battalions, three corps artillery regiments, two 'Blackshirt' battalions, one anti-tank company, two mortar companies and one signals company. Also in Tobruk were the Regia Marina’s light cruiser San Giorgio and 2,300 men and two artillery groups of the Guardia alla Frontiera, as well as service, quartermaster and supply units.

Although Pitassi Mannella had 32 L3/35 tankettes and 39 M11/39 medium tanks, only seven of the latter were operational and in three weeks of repair efforts only three M11/39 tanks were made serviceable enough to move in an engagement. After it had become obvious in the autumn of 1940 that the L3/35 was obsolete and the M11/39 badly designed and prone to mechanical failure, the 21o Battaglione di carri armati leggeri and part of the 1o Battaglione di carri armati medi had departed for Benghazi for re-equipment with the new M13/40 medium tank. Pitassi Mannella had received no spares or fuel for the tanks, and therefore had the lightly armed and thinly armoured L3/35 and the M11/39 vehicles buried in the sand as strongpoints.

Pitassi Mannella divided the defensive perimeter in two sectors, five sub-sectors and 16 strongpoints. Generale di Brigata Umberto Barberis’s Eastern Sector controlled Sub-sector A from the sea to Bir Junes to block the road from Bardia with four strongpoints, and Sub-sector B to block the road from El Adem with two strongpoints. The first line of the Eastern Sector was manned by the troops of the Guardia alla Frontiera reinforced with four companies from the 69o Reggimento fanteria. Expecting the main attack from this direction, Pitassi Mannella established a second line of defence 2 to 4 miles (3.2 to 6.4 km) behind the strongpoints, based on a small hill at the junction of the El Adem and Bardia roads. On the second line every available tank was dug in as a strongpoint. Between this position and the sea the 3/69o Reggimento fanteria was sited.

General di Brigata Vincenzo dalla Mura’s Western Sector controlled Sub-sector A in the desert to the south of Tobruk with four strongpoints, Sub-sector B to block the road from Acroma with three strongpoints and Sub-sector C to block the road from Derna with three strongpoints. Sub-sectors A and B were each defended by one battalion of the 70o Reggimento fanteria, while one 'Blackshirt' battalion manned Sub-sector C. Behind the first line of defence were five strongpoints manned by the 3/70o Reggimento fanteria, which doubled as the reserve unit for the three battalions in the first line. The commander of the 69o Reggimento fanteria received the reserves Pitassi Mannella could muster, an understrength tank company with seven M11/39 medium tanks, and two ad hoc units consisting of one Bersaglieri motorcycle company, one infantry company, one machine gun platoon, one anti-tank platoon and one anti-aircraft section each. In front of the strongpoints 11 miles (18 km) of anti-tank ditch were cleared, and totals of 7,000 tripwire mines and 16,000 pressure mines were laid. To make up for the lack of anti-tank mines, Pitassi Mannella had 2,200 26-lb (12-kg) bombs and 800 33-lb (15-kg) bombs left by the Regia Aeronautica and now buried upright in the desert in the hope that a British tank passing over them would trigger the impact fuse.

Pitassi Mannella organised the artillery into three groups, two for the Eastern Sector with 123 guns and one for the Western Sector with 97. On the correct assumption that the British-led forces would attack from the south, Pitassi Mannella sent the 2/Reggimento di artiglieria and 3/Reggimento di artiglieria groups with 75-mm (2.95-in) 75/27 field guns, and the 105o Reggimento di artiglieria and 130o Reggimento di artiglieria groups with 149-mm (5.87-in) 149/13 heavy field howitzers and one battery with 75-mm (2.95-in) anti-aircraft guns (used as anti-tank guns) into that area. For long-range artillery fire, Pitassi Mannella relied on the elderly cruiser San Giorgio in Tobruk harbour: she had two twin 254-mm (10-in) guns and four twin 190-mm (7.48-in) guns. Two Regia Marina shore batteries had twin 120-mm (4.72-in) naval guns and two mobile 149-mm (5.87-in) heavy guns of the Guardia alla Frontiera.

Lacking air reconnaissance, Pitassi Mannella was unaware of the British artillery positions, and as most British artillery had a longer range than the Italian artillery, which was mostly of World War I vintage, was little chance of effective counter-battery fire. Pitassi Mannella decided to employ every gun capable of direct fire as anti-tank artillery and managed to assemble 110 anti-tank guns: 32 37-mm guns in the buried M11/39 tanks, 43 47-mm anti-tank guns, 13 65-mm (2.56-in) mountain guns, 21 75-mm (2.95-in) field guns, one 76-mm (2.99-in) naval gun found in the naval stores. Armour-piercing ammunition was available for only the 37-mm and 47-mm anti-tank guns.

After surrounding Tobruk, the Western Desert Force had exhausted the ample Italian supplies it had captured at Capuzzo and Sollum. O’Connor directed that the supplies delivered through the port of Sollum, at the rate of 350 tons per day early in January and 500 tons per day thereafter) to the 10^th and 11^th Field Depots he had set up about 43 miles (70 km) to the east of Tobruk. Concerned mostly about not having enough fuel and supplies for the offensive after the fall of Tobruk, O’Connor delayed the attack for the accumulation of more supplies. As the 7^th Armoured Division had suffered more losses than the Australian 6^th Division, O’Connor decided that the Australians would lead the attack. The two most depleted units, the 8^th King’s Royal Irish Hussars and the 6^th Royal Tank Regiment, were withdrawn and their equipment distributed to the other four regiments of the armoured brigades. The first wave of the attack was to be the Australian 16^th Brigade and the 7^th Royal Tank Regiment, followed by the Australian 17^th Brigade and the Australian 19^th Brigade. The 7^th Armoured Division was to attack along the Western Sector and perimeter to pin down the defenders. On 19 January the Royal Air Force dropped leaflets calling on the Italians to surrender, but Pitassi Mannella ignored this blandishment.

From 00.00 to 02.00 on 21 January, the Royal Navy’s monitor Terror and three smaller gunships bombarded Tobruk, while destroyers waited farther offshore to attack San Giorgio should her crew attempt to escape. For the rest of the night Vickers Wellington twin-engined medium bombers attacked the port installations and defensive positions, and their engines drowned the sound of the British tanks assembling for the attack.

At 05.40 the British artillery opened fire along the entire line, concentrating on a rectangular area about 765 by 875 yards (700 by 800 m) where the Sub-sectors A and B of the Eastern Sector met. Under cover of darkness, Australian sappers and the British artillery fire cleared a path through the thin Italian minefield in the area, and at first light the Australian 2/3^rd Battalion attacked and, within an hour, had created a breach 1 mile (1.6 km) wide. At 07.00, 18 Matilda II infantry tanks passed through the breach, three veering left with the Australian 2/3^rd Battalion, while another three veered right with the Australian 2/1^st Battalion to expand the breach. At the same time, the other 12 Matilda tanks advanced with the Australian 2/2^nd Battalion toward Tobruk. The first unit to be overrun by the 2/2^nd Battalion was an artillery group, which had no time to lay its guns for direct fire before it was overrun.

The Italian units' lack of radios proved to be a severe disadvantage, for their telephone lines had been cut by the British air and artillery bombardment, and Pitassi Mannella received notice of the British attack only between 08.30 and 08.45 from a despatch rider. By 09.10 the Australian 2/2^nd Battalion had reached Sidi Mahmud and the Australian 2/1^st Battalion was at Sidi Daud. The Australian 17^th Brigade with the Australian 2/6^th Battalion and Australian 2/7^th Battalion had captured the Italian artillery positions between the two points. By 10.30 the Australians had overrun four of the Italian strongpoints and destroyed six of the 10 artillery groups in the area. At 08.30 the Australian 19^th Brigade, supported by A Squadron of the Australian 6^th Division Cavalry Regiment, had started to move on the 4o Reggimento carri. The Australian brigade was supported by 78 field guns, which moved in turns 220 yards (200 m) forward every two minutes. The Australian 19^th Brigade struck the 3/69o Reggimento fanteria, which was quickly overrun. A Bersaglieri company and three M11/39 tanks that tried to plug the gap in the second line were defeated within minutes, and all three M11/39 tanks were knocked out.

By 11.50, Pitassi Mannella had informed Graziani that the Eastern Sector had been destroyed and only isolated positions held out. All Graziani could do was to send three Fiat CR.30 single-engined biplane fighters to Tobruk, where all three were promptly shot down by the RAF. Between 12.00 and 14.0, the Australian 19^th Brigade attacked the position of the 4o Reggimento carri with a ferocity so great that 70% of the officers, including both battalion commanders, and 50% of the troops were killed in action. During the day, Bristol Blenheim twin-engined light bombers of the RAF’s Nos 55 and 113 Squadrons flew 56 sorties against Tobruk and the Gloster Gladiator and Hawker Hurricane single-engined fighters of the RAAF’s No. 3 Squadron and he RAF’s Nos 73 and 274 Squadrons patrolled to the west.

At 13.00, Pitassi Mannella ordered the mobile reserve, with the seven operational M11/39 tanks, to attack the Australian left flank from behind an artillery barrage. Two Australian anti-tank guns and two tanks destroyed five of the seven Italian tanks, and when Australian infantry pushed forward the mobile reserve surrendered. At 16.00, the Australian 2/8^th Battalion attacked the Pilastrino position, while the Australian 2/4^th Battalion reached and surrounded the Italian headquarters at the abandoned Fort Solaro. Pitassi Mannella and his staff retreated into the cellars but by 18.30 Pitassi Mannella had ordered his staff to surrender. At the same time the 6^th Divisional Cavalry Regiment had reached the outskirts of Tobruk but then been stopped by fire from San Giorgio. Men of the Australian 2/4^th Battalion moved down the cliffs and used 3-in (76.2-mm) mortars against San Giorgio. Having lost contact with forces outside of Tobruk, Contrammiraglio Massimiliano Vietina organised the defence of the harbour with the few men at his disposal. Graziani had denied the admiral’s request to make a sacrificial attack on the British warships outside the harbour, and Vietina began systematically to destroy the harbour and its stores.

By the fall of night half of the Tobruk fortified area had been captured, and at 04.15 on 22 January, Vietina ordered Capitano Stefano Pugliese to detonate San Giorgio's magazines. Mackay ordered a general advance for the morning of 22 January, and at 08.30 Vietina surrendered to Robertson of the Australian 19^th Brigade, followed shortly afterward by della Mura, who surrendered with the remnants of the Pilastrino position. At 16.00, the last strongpoint surrendered and Tobruk had fallen.

Most of the demolitions had been of stores rather than installations. The British inshore squadron immediately began minesweeping operations and opened the port on 24 January.

The Italians had suffered more than 24,000 casualties: 18 officers and 750 other ranks had been killed, 30 officers and 2,250 other ranks had been wounded and more than 20,000 men had been taken prisoner. The British captured 208 pieces of artillery and 87 tanks, and the XIII Corps, as the Western Desert Force had now been designated, had suffered 400 casualties, 355 of them Australian.

By the time of the Italian surrender, O’Connor’s divisions had already pressed on, the 7^th Armoured Division reaching Mechili and fighting the action at Mechili on 24 January, while the Australian 6^th Division had reached the Italian forward positions at Derna on the same day.