"Rat" or Miles Ratledge was the first Napalm Death drummer playing between 1981 or 1982 and 1985. He recorded the participation on the Bullshit Detector compilation with the band. Miles Ratledge left in 1985, after recording the classic "Hatred Surge" demo. He was replaced by Mick Harris.
Rumours said Ratlegde was admitted to a mental institution, and Mark Greenway has said that he has become a monk or something. Miles is actually alive and well and living in Denmark, were he studies anthropology.
The fact is that he didn't really want Napalm Death to become a fast and furious thrash band, but he wanted it to be more among the lines of post-punk bands like the Southern Death Cult. Justin and Nik got fed-up with him and invited Mick Harris to join ND and take Rat's place around September 1985.