Brigadier Rattan Kaul was commissioned in 4/5 Gorkha Rifles {Frontier Force}, where he served for nearly 25 years. He commanded 4/5 GR {FF} for nearly four and a half years and was the first CO in the Regiment, since 1927, to command in the rank of Colonel. As a young Captain, he took part in 1965 War against Pakistan with his unit. In Nagaland he, in a raid, accompanied by only few of his men, apprehended Chief Secretary to then Underground Self Styled President of Nagaland {NSCN}, from his hideout. During Bangladesh War 1971, as an assault Rifle Company Commander he led his company in a Khukri assault on a Company of 31 Punjab Pakistan Army at Atgram {Sylhet District- East Pakistan; now Bangladesh}.

In first ever heliborne operation of Indian Army, conducted by 4/5 Gorkha Rifles {Frontier Force} on 7 December 1971, the battalion of approx 400 men landed, amidst two Pakistani Brigades defending Sylhet town. The unit, without any ground link up till 15 December, broke the spine and resistance of the Pakistani troops, resulting in their negotiating surrender on 15 December, even before the temporary ceasefire and garrison formally surrendering on 16 December morning; much before the surrender at Dacca in the evening of 16 December. Brigadier Kaul, then a major, was forward rifle company commander and was seriously injured in the Battle of Sylhet.

In 1974 he was amongst top ten officers to be selected for Staff College, for a year long professional course at Wellington. Apart from foreign assignment with his battalion, he was Instructor Training Team Infantry School, Brigade Major, Colonel General Staff of a Division and Instructor Senior Command Wing, War College. He commanded an infantry brigade in Punjab, during militancy and was awarded COAS Commendation for his exceptional work in Khem Karan Sector.

An HRD, Management and Defence Analyst, he was also visiting lecturer to Air Force, Naval Higher Command Courses and IMS Indore. He has many books on military history and plethora of articles on History, Defence Concepts and Kashmir Centric papers to his credit. In 1997 he stepped into Industry and served as Vice President, Birla's. He was the one to bring, for the first time in more than 70 years, latest photograph of more than 1000 years old Sharda Temple in Pakistan Occupied Kashmir and share it with Goddess Sharda's worshippers in India.