Passalacqua") is an inactive tank battalion of the Italian Army, which was based in Solbiate Olona in Lombardy and last operationally assigned to the Mechanized Brigade "Legnano".

The unit's lineage traces back to the World War II IV Tank Battalion M13/40, which was formed in October 1940 by the depot of the 32nd Tank Infantry Regiment and attached to the 131st Armored Division "Centauro" for the Greco-Italian War.

In April 1942, the battalion was transferred to the 133rd Tank Infantry Regiment, with which it deployed to Libya for the Western Desert campaign.

The battalion's anniversary falls, as for all tank units, which have not yet distinguished themselves on the battlefield, on 1 October 1927, the day the tankers speciality was founded.

In late March 1941 the Centauro division moved, in preparation for the Invasion of Yugoslavia, to Shkodër in northern Albania.

On 17 April the Centauro reached Trebinje, where it met up with units of the 133rd Armored Division "Littorio", which had advanced southward from Istria.

On 8 December 1942, the 133rd Tank Infantry Regiment and its battalions were declared as lost due to wartime events.

The regiment was declared lost due to wartime events on 18 April 1943 after the Battle of El Guettar.

Tank and armored battalions created during the 1975 army reform were named for officers, soldiers and partisans of the tank speciality, who had served in World War II and been awarded Italy's highest military honor the Gold Medal of Military Valor.

The 4th Tank Battalion was named for Lieutenant Ugo Passalacqua, who, as commanding officer of a company of the IV Tank Battalion M13/40, was gravely injured on 27 January 1941 during combat near Klisura Pass and died from his wounds at the Italian field hospital in Vlorë on 10 February 1941.

[1][4] On 12 November 1976 the President of the Italian Republic Giovanni Leone granted with decree 846 a new flag to the battalion.

[1][5] After the end of the Cold War the Italian Army began to draw down its forces and on 1 June 1991 the 3rd Mechanized Brigade "Goito" was disbanded and the 4th Tank Battalion "M.O.

The same year the 67th Mechanized Infantry Battalion "Montelungo" moved from Monza to Solbiate Olona.