In a game I had two subs sent at me very close together, one of 117 drillers, one of 105. My plan was to degrade his subs with what I call 'missiles' (unescorted specialists using the generals ability to kill 10 drillers a time). The first specialist hit killed 10 drillers on the first sub and was captured. It continued towards my opponents outpost but when it met my opponents second sub that sub turned around and headed back to its outpost, the specialist was not a sabotuer.
This only happened when I had multiple 'missiles' travelling on the same line, when it was just one the captured specialist did not effect the second sub.