Infinitive sentence question

Imperator militibus subsidium ____________________(submitto, submitti, submittere) cupiverat.

This is the question in Caesar a legamus transitional reader. The key says that submitti is correct and the sentence should be translated this way:

The general had wanted aid to be sent to the soldiers.

Why can’t submittere be correct and the sentence translated this way:

The general had wanted to send aid to the soldiers.

I’m sure there is some obvious reason that I’m not seeing.

Thank you!

I think you’re right, Matermultorum, that “submittere” could be said unless the context requires the passive and relief is to be raised by someone else, perhaps nearer to the soldiers than Caesar.

Rectè dicis, Matermultorum, “submittere” grammaticè dici posse, nisi contextus passivam vocem requirat et Caesar alium in militum vicino subsidium submittere cupivisset.

Thank you!

You’re welcome!
Non est cur mihi gratias agas, Matermultorum!