With officers in night, he would march to the canteen like a guardsman. (Annotate)

With officers in the (a) night, he (b) would march to the canteen (c) like a guardsman. (d)

(a) The article "the" is missing before the word night.

(b) "he" is the subject of this sentence. The subject is rather undefined, vague, and needs to be investigated for one to have a clearer understanding of what this snippet is all about.

(c) "the canteen": This is another mystery noun in the above sentence. It begs the question of location. It also raises the question of why the "he" would match off to a canteen in the night.

(d) "like a guardsman": This is a simile that electrocutes the imagination. In this sentence, the three words above, besides acting as a simile and imagery (both of which are literary tools), functions as an Adverbial Clause which serves to qualify the verb march.

The only instruction given in the question is to Annotate.

To annotate means to give more meaning to, to explain, to interpret, or to make more meaningful.

Please note that an adverbial clause is a dependent clause that while functioning as an adverb, qualifies another adverb, a verb, or even an adjective.

By way of further annotation, it suffices to say (with respect to the Grammatical Person) that the sentence above is reported in the third person singular.

For further information about annotation please see the following link: