You may want to read "Hijack SQ117 - the untold story" by Sumiko
Tan. The book has some photos.
I believe the team that went into the plane had MP5s, as described
in the book. The others involved on the ground - eg. securing
passengers, parameter defense, etc. had M16s, etc.
I was doing my NS back then, on the night of the hijack - it so
happens that my company were on 2NTM. I think there were a number
of units on that particular day.
Also, during the SOF recruitment briefings, they came with some of
their equipment and had MP5s.