What do you mean by SOS basis?

The letters SOS in Morse Code mean HELP.

'SOS' is the Morse code international distress signal. 'We require the material on an SOS basis...' means on 'an emergency basis...'.

On the other hand, sos is a medical abbreviation that means "as needed," which would give an answer almost opposite to the original answer. Ah, the hazards of abbreviations!