ATTACK.BIN is one of two lumps that contains attack data. DT6 is the other.
ATTACK.BIN is a headerless binary file. Its record length in INTs is defined by the first INT in BINSIZE.BIN. It is therefore easily expandable.
The nth attack has the first 40 INTs/80 bytes of its data stored in the nth record of DT6, the remaining data stored in the nth record of ATTACK.BIN, which is combined into a single array when loaded. The complete specification combining data from both lumps can be found at DT6 #Complete Attack Data Formal Specs. Only offsets 40 and up are stored in ATTACK.BIN.