Understanding the Kanji
If you are to be able to read Japanese, you need to have a fundamental understanding of the Kanji.
The first important thing to understand is that, although each character does have one or numerous general meanings, the actual meaning of an individual Kanji depends on the context.
Which brings us to the second important thing to understand: in Japanese, words written in Kanji are often composed of two, three or sometimes more Kanji. In other words, the three Kanji: 部, 隊 and 長 do not mean a word separately, but rather a single word that is composed of three different Kanji.
In other words, although 部 does have a general meaning of “section" (as in a part of something), you really understand its purpose when you see with which other Kanji it is used with, in this case 隊 and長 (this is what I meant by the importance of context).
Indeed, by looking up 部隊長 in a dictionary you will find that it is a Japanese word which can be translated as a sort of commanding officer (translated as Lord Commander in the English version of Final Fantasy IV).