Lusitania's resting place has always been know. It simply wasn't dived on out of respect as a war grave.303 was loaded with cordite, a propellant known for very rapid degradation.
The sad fact is people are still killed by unexploded ww1 and 2 munitions and anti personel land mines are a major killer and maimer of epeoples in spite of e late Princess Dianna's work toward their elimination.