Project 633 was a further development of the Soviet navy's post-war 611 (Zulu-) and 613 (Whiskey-class) designs, which themselves were derivatives of the German Kriegsmarine Type XXI submarine.

By today's standards Romeo class submarines are considered obsolete, but they still have some value as training and surveillance vessels.

Under the 1950 Sino-Soviet Friendship and Mutual Assistance Treaty, the Soviets passed to China (and later to North Korea) the documentation necessary to produce Romeo submarines in 1963.

A total of 84 Type 033 submarines were built in China from 1962 to 1984, plus several exported to other countries.

Today most of the Type 033 subs have been retired or preserved, with a few remaining in service for training purposes.