Was is used in the first person singular (I) and the third person singular (he, she, it). Were is used in the second person singular and plural (you, your, yours) and first and third person plural (we, they).

Both “was” and “were” can be used as the past tense of “to be,” but they are not interchangeable. Was is used for the first-person singular (e.g., “I was”) and third-person singular (e.g., “she was”). Were is used for the second-person singular (e.g., “You were”) and all plural forms (e.g., “They were,” “we were”).

Both 'personnel were' and 'personnel was' can be correct depending on the context. 'Personnel were' is used when referring to a group of people working in an organization, while 'personnel was' is used when referring to the concept of personnel as a singular entity.