The Viking rocket engines were members of a series of bipropellant engines for the first and second stages of the Ariane 1 through Ariane 4 commercial launch vehicles, using storable, hypergolic propellants: dinitrogen tetroxide and UH 25, a mixture of 75% UDMH and 25% hydrazine[3] (originally UDMH).

By 1971, the thrust had improved to 540 kN, with resulting engine named Viking 1 and adopted for the Ariane program.

The engine first flown on the Ariane 1 rocket in 1979 was Viking 2, with thrust further improved to 611 kN.

The first failure (on second Ariane 1 flight 23 May 1980) was due to a chamber combustion instability.

The second failure was of human origin: a rag had been left in a water coolant pipe during installation, resulting in a loss of thrust and vehicle breakup due to off-centre thrust during launch on 22 February 1990.