I think the whole reason he needed the Dead was because the Corsairs of Umbar were going to be able to hit Gondor from an unexpected side, which would pretty much be a kill-shot to an already overwhelmed city. He fell to his knees because he saw the extent of the fleet, and despaired for Gondor, having failed to save them from the fleet.
On my middle earth map there is no Umbar, just the "city of the corsairs". Then when looking online I came across a middle earth map that cited Umbar as a region rather than a city.
Is Umbar a city or a region? - Science Fiction & Fantasy Stack Exchange
: being the member of a pair of similarly spelled vowel or vowel-containing sounds that is descended from a vowel that was short in duration but is no longer so and that does not necessarily have duration as its chief distinguishing feature
SHORT definition: 1. small in length, distance, or height: 2. used to say that a name is used as a shorter form of…. Learn more.
Define short. short synonyms, short pronunciation, short translation, English dictionary definition of short. adj. short er , short est 1. Having little length; not long. 2. Having little height; not tall. 3. Extending or traveling not far or not far enough: a short...
Short, brief are opposed to long, and indicate slight extent or duration. Short may imply duration but is also applied to physical distance and certain purely spatial relations: a short journey.Brief refers esp. to duration of time: brief intervals.
short (third-person singular simple present shorts, present participle shorting, simple past and past participle shorted) (transitive) To cause a short circuit in (something).