When a warship like the USS John S. McCain turns off the Automatic Identification System (AIS), no crucial information such as its identity will be known to merchant ships in the vicinity.
Former Royal Australian Navy (RAN) commodore Sam Bateman told The Straits Times yesterday that he believed the US guided-missile destroyer had disabled its AIS.
Said Dr Bateman, who served 39 years in the RAN and commanded four navy ships in 10 years: "I would think the McCain probably did not have its AIS switched on.
"Warships often don't have their AIS switched on because of security reasons."
The AIS - which is also commonly used by merchant vessels - provides information on ships, such as their identity, call-sign, direction and speed.
In an emergency situation, where two vessels find themselves on a collision course, being able to identify each other is crucial, said Dr Bateman.
Stressing the need to not solely depend on technology, he said he made it a point to train young officers to develop some sense of "situational awareness".
This means the ability to judge the relative distances of other ships, take compass bearings, judge their positions at sea and look out for navigational marks.
The collision between the US destroyer and Liberian-flagged tanker Alnic MC took place near Pedra Branca.
It is a busy area where ships enter and leave the Singapore Strait through what is known as the Traffic Separation Scheme, said two master mariners.
Said Captain Mohd Nasir Umari, 50, who has 30 years of sailing experience, including piloting tankers near Pedra Branca: "Sometimes, you can have six to eight ships all converging at the same time.
"This is where we need to be most alert and evaluate targets (on the radar) near you.
"Sometimes, you can see the other ship's lights, but in poor visibility, you will not know how big that vessel is. So, that is when we slow down to manoeuvring speed."
At manoeuvring speeds of about 10 knots, or roughly less than 20kmh, a tanker can still react and take evasive action, said Captain Tony Goh.
The 68-year-old, who began sailing in 1967, said: "Any vessel moving at more than 20 knots in a busy area would be just too fast."