What part of speech is sorties?

Sorties can be categorized as a noun and a verb.

Parts of speech

1. sorties is a verb, present, 3rd person singular of sortie (infinitive).
2. sorties is a noun, plural of sortie.

Verb
sortie - To sally.
Noun
sortie - (military) an operational flight by a single aircraft (as in a military operation)
sortie - a military action in which besieged troops burst forth from their position