What is lifeboat storm oil?

Supposedly, some lifeboats were supplied with 'storm oil' for the purpose of calming seas. The presence of oil in seawater does reduce the effects of friction / wind resistance and causes calmer conditions:

a) the 'chum slick' left by chum (or bait) when fishing is a visibly calmer trail in the water where the oils from the bait have drifted

b) slicks can be left in the wake of motorboats where small amounts of motor oil / residue are released into the water

c) the presence of natural algae in seawater also releases some oil and marginally calms the sea in windy conditions