When the patrol ambushes the first Japanese patrol, there are five Japanese in this patrol. Hornsby shoots one in the back, causing him to fall to the ground. The rest of the British troops then fire at the remaining Japanese, of which there are still five standing.
When Lt. Lawson confers with Col. Thompson in the HQ, the Union Flag on the wall behind Col. Thompson is upside down. In another shot, it is up the right way. During the shoot at Cubi Point in he Philippines, someone stole the flag sometime during the night. They had to send to Hong Kong for another one and the new one was replaced the right way up.
When Pvt. Jock Thornton is knifing a Japanese, we see him stab the soldier several times in the lower right side of his back. Later on we see same the soldier lying on the ground, but he is only bleeding from what looks like a single wound in the middle of his back.
The British Vickers machine gun had an effective range of 810 yds (740m), but could be used for indirect fire at distances up to 4500 yards (4100m). The British 2-inch mortar had a range of 500 yards (457m). Given that the mortars can reach the edge of the jungle, that gives the width of the open field as around that distance (500 yds). The Japanese Arisaka rifle had an effective range of 400m (360 yds), which would put the British troops out of range. However, the Japanese infantry are seen using a Type 99 Light Machine Gun. This had a range of up to 1600 yds (1500m), though its effective range was more likely considerably less. This means that the British soldiers would not be out of range of this weapon when they stood behind their weapons pits, though it is unlikely the Japanese would try to hit them at that distance.