The Chief Minister thanked India Post Office for its services. Wednesday was the National Post Day.
"Nothing can beat the feeling of receiving a letter from home while in the army! It used to be driving force during my army days & these letters brought both tear & smile," Singh, 77, tweeted.
Posting a black and white picture of his days in the army, he said: "I salute @IndiaPostOffice for their services to the nation & thank them for the memories."
The two-time Chief Minister, a scion of the erstwhile Patiala royal family, is also a military historian. Singh had served in the second battalion of the Sikh Regiment between 1963 and 1969.
Though he left army for a short period in between, to look after the family responsibilities, his love for the army brought him back when the India-Pakistan war broke out in 1965, an army officer close to him told .
His father Lt. General Maharaja Yadavinder Singh served the regiment in 1935 and was Colonel of the 2/11 Royal Sikhs from 1938 to 1950, and of the 2 Sikhs between 1950 and 1971.
Singh's grandfather Major General Maharaja Bhupinder Singh was Colonel of the 15th Ludhiana Sikhs during 1918-1922 and then of the 2/11 Royal Sikhs in 1922-1938.
His book, 'Honour and Fidelity: India's Military Contribution to the Great War 1914-1918', talks about the contribution of Indian soldiers, presented a silver memento a replica of a Sikh regiment soldier in full battle attire to the battalion, which will be displayed at the Officers Mess.
( With inputs from IANS )