armyhospitals were filled with injured men
Full is an adjective, and means ‘containing a lot’:
The theatre is completely full this evening.
The room was full of books.
Fill is a verb, and means ‘make or become full’. The -ed form is filled:
Can you fill this bottle with water for me?
She has filled my life with happiness.
We use the -ed form + with as an adjective especially in metaphorical contexts to refer to strong emotions:
She looked at him, filled with horror.