The regiment is part of the Italian Army's infantry arm and assigned to the Airmobile Brigade "Friuli".

The 65th Infantry Regiment's IV Battalion was also formed in Sicily with four companies provided by the 2nd Provisional Depot in Palermo.

In 1895-96 the regiment provided seven officers and 230 enlisted for units deployed to Italian Eritrea for the First Italo-Ethiopian War.

At the time the 66th Infantry Regiment consisted of three battalions, each of which fielded four fusilier companies and one machine gun section.

[5][9][11][12] At the outbreak of World War II the regiment consisted of a command, a command company, three fusilier battalions, a support weapons battery equipped with 65/17 infantry support guns, and a mortar company equipped with 81mm Mod.

On 18 November 1941 the British Eighth Army launched Operation Crusader to relieve the siege of Tobruk.

On 24 November, General Erwin Rommel ordered the Afrika Korps and 132nd Armored Division "Ariete" to push east to relieve the Siege of Bardia and the Axis frontier garrisons, while the Trieste division was sent South to cover the right flank of Rommel's advance.

On 6 December the Axis forces received the order to retreat westwards and the Trieste division formed the rearguard and fought delaying battles at Bir Bellafaa, Sidi Breghish, Alem Hamza, and Suluq.

On 21 January 1942 Panzer Group Africa attacked and drove British forces back to Ain el Gazala.

On 26 May 1942 Axis forced commenced the Battle of Gazala, during which the Trieste division was ordered to open a gap in the minefield north of the Bir Hakeim.

The division then pursued the retreating British forces and clashed with rearguards at Sidi Omar, Mersa Matruh until reaching El Alamein in Egypt.

[13] The division lost two regimental commanders before being partly overcome by British attacks, but the delay of the Allied advance allowed German armored forces to launch a devastating counterattack.

On 23 October 1942 the British commenced the Second Battle of El Alamein and the Trieste initially formed the reserve in the North of the Axis line.

On 4 November the division's command and most of the 66th Infantry Regiment "Trieste" retreated to Fuka and thus escaped the destruction of Axis forces at El Alamein.

[5][8][9][12] The remnants of the German-Italian Panzer Army retreated to El Agheila, where on 26 November 1942 the Trieste's two infantry regiments were reorganized and brought back up to combat strength by accumulating the survivors of other divisions.

In 2004 the regiment was deployed to Nasiriyah in Iraq, where it fought a heavy battle with Iraqi insurgents on 7 and 8 September 2004.

[1][2][15] In 2008 the regiment was deployed to Herat Province in Afghanistan as part of Italy's contribution to NATO's International Security Assistance Force.

The Maneuver Support Company is equipped with 120mm mortars and Spike MR anti-tank guided missiles.