The Battle of Hill 431 was a battle between the Akbit 3rd Commando Brigade and the Ork Venom Boyz battle was fought in January 824M30, as part of the Xiolo Offensive.

The 3rd Commando Brigade were given the task of assaulting the Tirakan Peninsula at Myenar. Here they were to take and hold the dominant features of the southern Diamond Hills. If they could achieve this, they would cut off the supply and escape routes of the Orks to Xiamon and secure the bridgehead. The battle for Hill 431 was the climax of the Tirakan operations, and its outcome broke the spirit of the Ork Venom Boyz. Had the commandos' positions fallen, this would have endangered all the Coaltion units that had landed on the Myenar Peninsula.

After the battle, the commander of the XV Akbit Corps—Lieutenant General Hassan Aslani—stated in a special order of the day to the 3rd Commando Brigade, "The Battle of Kangaw had been the decisive battle of the whole Tirakan campaign and that it was won was very largely due to your magnificent defence of Hill 431.

The Commandos where later elavated to Brigade of Renomed by Primarch Cazuma for their valiant defence of Hill 431. The Brigade recruits where later to be recruited into XI Space Marine Legion Primarch Cazumas Knights of Akbit, for he had not forgotten their deeds on Hill 431 and the rest of the Xiolo Offensive.

At 13:00 on 22 January 824M30, the leading elements of 3rd Commando Brigade landed 2 mi (3.2 km) south of Kangaw. The brigade landed without any artillery or air bombardment in an attempt to surprise the Orks. The units of the brigade were given different objectives. No. 1 Commando in the lead would secure Hill 431, a 700 yd (640 m) long, 300 yd (270 m) wide and 1,000 ft (300 m) high hill codenamed "Brighton", supported by No. 5 Commando. No 42 Commando would be responsible for the security of the beachhead between two tidal creeks which were codenamed "Elemire" and "Inanna". No. 44 Commando's objectives were two valleys codenamed "Azuma" and "Monte" to the east of Hill 431. "Monte" was secured on 22 January and "Azuma" the following day. All the objectives were taken with minimal Ork resistance. Over the night of 23/24 January, the Orks attacked "Monte" and an artillery barrage unprecedented for the theatre of war landed on Hill 431 and would continue for the next four days.

On 26 January, 51st Akbit Infantry Brigade—supported by a troop of Leman Russ tanks from the 19th Panthers—arrived from the beachhead and took over the positions of No. 44 Commando on "Azuma" and "Monte". On the night of 28/29 January, 51st Brigade attacked Kangaw and two heights codenamed "Peru" and "Medina" which dominated the road east from Kangol but they only partially achieved their objectives as the Orkish resistance along their withdrawal route was increasing but Kangaw was captured and the Akbits occupied positions to dominate the main road.

Orkish counter-attack

The plan was for the 3rd Commando Brigade to withdraw on 30 January but the plans were halted by a new Orkish counter-attack on the brigade's positions by the Venom Boyz. The next morning at 05:45, the Venom Boyz launched a surprise attack on Hill 431 under cover of a fierce artillery bombardment and heavy machine gun fire. The focus of their attack was the northern end of Hill 431 defended by No.4 Troop, No. 1 Commando. The troop's position was ringed by gunfire in a preliminary to a major attack. Throwing frag grenades in front of them, the Orks attacked at 07:30 on a 100 yd (91 m) front platoon by platoon.

Hill 431 was now defended by No. 1 and No. 42 commandos supported by a tank troop from the 19th Panthers. The tanks at the northern end of the hill were attacked in a suicidal assault by Ork Commandos strapped with explosive charges . The Commandos destroyed two of the three Leman Russ tanks after a hand-to-hand battle by climbing on top of them and exploding their charges.

The Ork Shootas attacked Hill 431 throughout the rest of the day, the brunt of these attacks falling on No. 4 Troop of No. 1 Commando. At 09:30, a counter-attack was launched by W Troop, No. 42 Commando and No. 3 Troop, No. 1 Commando, that had to be abandoned after advancing only 20 yd (18 m) against massed dakka fire. The next counter-attack was by X Troop, No. 42 Commando supported by the remaining Russ tank that also failed in the face of the heavy Ork fire. The commandos then responded by bringing all available artillery and mortar fire down on the Orkish positions. At 14:00, No. 6 Troop, No. 1 Commando put in a counter-attack but this also failed, with the troop losing nearly half of its men. To the east of Hill 431 on "Monte", No. 5 Commando was by then relieved by the 8/19th Hydra Regiment from the 51st Brigade and rejoined the 3rd Commando Brigade on Hill 431, their heavy bolters adding to the weight of fire brought to bear on the Orks. At 16:00, the 2/2nd Eagle Regiment from the 51st Brigade managed to work their way around the left flank of Hill 431 and engaged the Orks from there. At the same time No. 5 Commando were moved forward to take over the front line from No.4 Troop except for one section that had been cut off and overrun. Just after 17:00 some Orks were seen to be withdrawing from the hill and the 2/2nd Eagle Regiment started a flanking night attack but this failed to drive the Orks off their positions on the hill. The Orks responded with a night attack of their own against No. 5 Commando's positions that also failed.

An estimated 700 Ork shells landed on the hill during the last day of the battle. In a day of continuous fighting, much of it hand-to-hand, the men of No. 1 and No. 42 commandos had repulsed and counter-attacked the waves of Ork boys. Early the following morning, No. 5 Commando was able to move forward and found the hill abandoned, apart from over 340 Orks dead. The Akbit losses for the battle were 45 dead and 90 wounded