A troopship is a large ship used to carry soldiers — usually a lot of them, and usually a long way. It is not a fighting ship. It does not attack anyone. Its job is only to move an army from one place to another, across a sea or an ocean. You meet this word mostly when people talk about the past, especially the two world wars. In those years, thousands of soldiers were put on one ship and sent to another country, and the trip could take weeks. Many old letters, films and songs are about that ship. So the word carries a feeling with it — leaving home, not knowing if you come back. Some troopships were built for the job. Many others were ordinary passenger ships that the government took over during a war, painted grey, and filled with beds. After the war they went back to carrying tourists. This is why people sometimes say a famous ocean liner "was a troopship" — for a few years, it was. Today armies mostly move soldiers by plane, so you will rarely see this word about now. It is a history word, and you will meet it in reading much more often than in speaking.

運兵船（軍隊運輸船）