4 / 73 ( Sphinx ) Special Observation Post Battery RA 4 / 73 ( Sphinx ) Battery is a battery of 5th Regiment Royal Artillery . It currently serves in the Surveillance and Target Acquisition ( STA ) Patrols role . History . 4 / 73 ( Sphinx ) Special OP Battery was formed in Germany in April , 1990 as part of 5th Regiment Royal Artillery . The Battery was formed by amalgamating the two separate Special OP Troops attached to the HQ Batteries of 5 Regt RA and 32 Regt RA . Q Battery was re - titled Q Headquarter Battery and 4 Battery & 73 Battery were merged with other locating Batteries in 5 Regt RA . The battery role was mooted in response to an identified capability gap in the surveillance of the Deep Battlefield . The " Depth Fire " concept proposed so - called " stay behind OPs " when it was identified that there was an inability to accurately assure heavy artillery deep into enemy territory . Along with being able to direct accurate artillery fire it would also mean that intelligence could be gathered at a tactical level on such things as headquarter locations , Main Supply Routes , reserve troop locations , vehicle concentrations and force numbers . The way in which this would be carried out was by inserting troops into hides , allowing the enemy to advance over them . Then , using their hides as mounting bases the troops would establish covert OPs to locate rear area locations and movements of enemy signature equipment . Due to its main role of directing artillery fire it was decided that this small , highly trained unit would be established within , and from Artillery units . One troop was first established in 1980 as part of 5 Heavy Regiment Royal Artillery , and later a second was formed when 32 Guided Weapons Regiment was re - rolled as the second Heavy Regiment . Initially a selection process was put into place by instructors and advisors who had experience in this field of work . After the bedding in period The Parachute Regiment were tasked to supply training instruction . 4 / 73 ( Sphinx ) Special OP Battery now recruit from all Arms . As the skills base and operational capabilities have evolved , once again the battery have a specialised Subject Matter Expert in place in order to provide and sustain the operational effectiveness of this highly motivated body of Surveillance Soldiers . Current role . 4 / 73 Battery is now regarded as a specialised unit to provide commanders with crucial battlefield intelligence on enemy positions . Members of this battery are volunteers who have passed a 20 week Special Observer Patrols Course . During Operation Herrick in December 2007 members of 4 / 73 Battery mounted the British Army ' s longest recorded desert patrol since World War II . During that tour two soldiers serving in the battery were killed : Tpr Jack Sadler HAC and Cpl Daz Gardiner REME . Insignia . Whilst most Gunners wear a dark blue beret , since 2008 soldiers of 4 / 73 Battery have changed to a Khaki beret to mark the close working relationship of the battery with the Honourable Artillery Company . Soldiers within the battery that have passed the STA Patrol Training selection course also wear the Special Observers badge on their arm as displayed above .