Although we don't have an example of the toy, at least I managed to find its origin. The Spacex Crash Tender is based on a pair of vehicles that briefly appear in a Thunderbirds comic strip by Frank Bellamy, published in TV21 nr 108 of 11 February 1967.
Appearing in only a few panels of the strip (see below), the crash tenders rush in to cool down a sabotaged fuel-transporting rocket toppled over inside its launching silo, while International Rescue are pumping out most of its cargo and need to rescue its crew before it explodes. But then the tenders' water supply runs out...
