What is underlying concept behind One Rank One Pension?

One Rank One Pension (OROP) in layman terms means "same pension, for same rank, for same length of service, irrespective of the date of retirement".

The demand for pay-pension equity, the underlying concept of OROP, was first brought to light after the decision by the Indira Gandhi-led Indian National Congress (INC) government, in 1973, two years after the historic victory in the 1971 Bangladesh war, and shortly after Field Marshal SHFJ Manekshaw retired, to decrease armed forces pensions by 20–40 percent, and increase civilian pensions by 20 percent, without consultation with armed forces headquarters.

In 1986, the Third Central Pay Commission (CPC) recommendations dint go very well among the rank and file of the armed forces with the Government's decision to implements Rank Pay, which reduced basic pay of captain, majors, lt-colonel, colonels, and brigadiers, and their equivalent in the air-force, and the navy, relative to basic pay scales of civilian and police officers.

The decision to reduce the basic pay of these ranks, implemented without consulting the armed forces, created radically asymmetries between police-military ranks, affected the pay, and pension of ten of thousands of officers and veterans, spawned two decades of contentious litigation by veterans. It became a lingering cause of distrust between the armed forces veterans and the MOD, which the government did little to ameliorate.