Commanders are responsible for incidents that happen on their watch regardless of whether they are aware, and they must be held accountable.

The responsibilities of high-ranking Singapore Civil Defence Force (SCDF) officers were set out during a testimony yesterday by Colonel Anthony Toh, commander of the 4th SCDF Division.

Taking the stand in the ongoing trial of two SCDF commanders linked to the drowning of Corporal Kok Yuen Chin, a full-time national serviceman, Col Toh said: "The commander on duty must walk the ground... The men would not have the opportunity to engage in horseplay because you could walk in on them anytime."

Responding to questions about the chain of command and responsibility in a fire station, he told the court that those directly involved in an incident would be held accountable, but the rota commanders would still bear overall responsibility for the actions of their men.

On May 13 last year, Cpl Kok, 22, drowned after he was pushed into the Tuas View Fire Station's pump well in a ragging incident to mark the completion of his national service.

The two on trial, Kenneth Chong Chee Boon, 38, a lieutenant, and Nazhan Mohamed Nazi, 40, a first senior warrant officer, were rota commander and deputy rota commander respectively. They were in charge of the station that night.

They were each charged with aiding a rash act that caused grievous hurt by illegal omission, and had allegedly failed to prevent a group of officers from making Cpl Kok enter the well.

In court, Col Toh, who has been with the force since 2005, said there were 11 reported cases of ragging in the SCDF from 2010 to 2017, of which one involved the "kolam" ritual, where officers entered the fire station's pump well.

He said the SCDF defined ragging as a physical or verbal act that would or is likely to "cause bodily harm, injury or mental anguish".

The court had earlier heard that Chong had been in the nearby control room when this happened. At one point, he stuck his head out of the room's window to tell them not to record any video of the incident.

In another video, a man identified as Nazhan is seen walking off after the group places Cpl Kok on the ground near the well.

Nazhan's lawyer suggested his client left the scene as he thought nothing would happen.

Col Toh said if a commander sees this and does not stop it, "he is not fit to be a commander".

"If (the commanders) see something that is not authorised and don't put a stop to it, it's an accident waiting to happen, and in this case it did happen."

The trial continues today.