North Vietnam, Ocean Crabs, August 19th, 1965, Michel Nr. 387-392; Six stamps with the nominals of 12 xu (four stamps), 20 xu and 50 xu were issued in perforated 11.0 and imperforate.
Here is the mint imperforate set:
Registered letter mailed to Klewitz in August 1968 featuring the entire perforated set. The overall postage of 1.18 Dong was slightly above the required postage for a standard registered letter to West Germany (1.10 Dong Tariff)
Registration Nr. 101140