Of course not, you idiot! The function of a vassal state is the complete opposite. A vassal state is required to provide military assistance to the dominant state when requested to do so, but it is not a requirement for the dominant state to defend the vassal state with its own military force.
If Trump goes to war with North Korea or China, our SAF (especially the medical team) must be on standby to be deployed when requested by USA. Our naval bases must be on standby to refuel & replenish US warships. Our air bases must be on standby to service US warplanes. It's the same with Australia and Japan.