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 and is currently 60 INTs/120 bytes. It is therefore easily expandable.
Each attack has 100 INTs/200 bytes of data. The first 40 INTs are stored in DT6, the next 60 INTs are stored in ATTACK.BIN. During runtime, the attack data is combined into a single 100 INT array. The complete specification combining data from both lumps can be found at DT6 #Complete Attack Data Formal Specs. Only offsets 40 - 99 are stored in ATTACK.BIN.