There was little hesitation when he saw five hostile Indonesian ships through his binoculars, speeding towards his vessel with their men ready for combat.
Quickly, then 25-year-old Lieutenant Roland Simon turned to the skipper of the ship next to his.
Lt Simon told him: "I will concentrate on the torpedo boats, you take the three smaller ones. We should sink as many boats as we can, and come to each other's aid as necessary."
For seven minutes, the two rivals sped towards each other, pointing their guns at each other.
This was in 1965, during the height of Konfrontasi when such encounters were par for the course.
That same year in March, his wife, who was pregnant with their first son then, had missed a public bus to the MacDonald House, escaping death when saboteurs bombed the building. Three people died in the attack which involved two Indonesian marines planting bombs at the building.
Mr Simon and his naval corp from the Malayan Royal Naval Volunteer Reserve's (MRNVR) Singapore division was all the country had to protect itself from naval intruders then.
The Republic of Singapore Navy (RSN) formed only two years later.
Made up of volunteers, the MRNVR served not only during Konfrontasi but also in World War II. Many, such as Mr Simon who retired as a major, later continued with the RSN.
Yesterday, 80 of these naval veterans - including five female veterans from the Singapore Women's Auxiliary Naval Service - gathered at a function room in Safra Toa Payoh to celebrate the 65th anniversary of the MRNVR's reconstitution and remember their fallen comrades.
The reunion is likely to be the last time they meet for such an event, said the unit's alumni adviser Adrian Villanueva, 77.
"Look at us, we are all so old already, I don't think there will be a 70th anniversary," he said.
The veterans, most of whom are in their 70s, recalled their experiences and pored over old photographs at the two-hour luncheon.
For Mr Simon, who is now 85 and wheelchair-bound, no photographs were needed to jog his memory of the incident.
"I never forgot. I was afraid," said Mr Simon of his encounter with the Indonesian ships.
Two were torpedo boats which could have easily sunk his World War II-era minesweeper vessel, the KD Langkasuka. The rest were Customs vessels. All five had entered Singapore's territorial waters.
The Singaporean and Indonesian vessels had a tense stand-off. Thankfully, three fighter aircraft from Tengah Airbase came to break up the stalemate.
Mr Simon's second son, who also attended the reunion, was all smiles when asked if he was proud of his father.
Said English teacher Ashley Mark Simon, 47: "Pride won't... be the word to describe how I feel about him. Few people have that kind of fortune to call their own father a hero."