The letters "l" and "d" and "l" and "d" sound very similar. However, it is important to distinguish the difference between words with "ld" and "lt". Sometimes the word does not even exist, and sometimes it is a different form of that word!
Lt. Geoghegan acts as a resource and a teacher for his soldiers by telling them how to protect their feet. He leaves them to perform the action instead of doing it for them. He also connects the soldiers with each other by having every person check another person's feet.
The captain tells the squadron that he is expanding it to four members, which concerns all of the lieutenants. Lt. Purcell states that four is an unlucky number because it's not prime. He then defines a prime number.