Learn French: Personne n'a pu débarquer avant minuit. - Nobody managed to disembark before midnight.

In the passé composé, pouvoir shifts in meaning from a general ability to a specific outcome. A pu implies that someone actually 'managed to' or 'succeeded in' doing something. With the negative Personne n'a pu, it emphasizes the specific event of failing to disembark. If it were the imparfait (Personne ne pouvait), it would just describe the background situation, meaning 'nobody was allowed' or 'nobody had the ability' to do it.

Why is there no pas to make the sentence negative?

The word personne (nobody) is a negative term that inherently replaces pas. When used as the subject of the sentence, it sits at the beginning and pairs with the negative particle ne before the conjugated verb, giving us the structure Personne ne... or in this case before a vowel, Personne n'.

How would the sentence change if personne were the object rather than the subject?

Here, personne is the subject ('Nobody managed...'), so it goes at the beginning. If it were the object (e.g., 'He didn't drop anyone off'), it would be placed all the way at the end, after the infinitive verb: Il n'a pu débarquer personne.

Is débarquer only used for getting off a boat or plane?