Sometimes the knowlege about IWC watches does not come from IWC in Schaffhausen but from collectors tracking down the details.
https://www.iwc.com/member/forum/search_all.asp?table=archives&sMessage=R.M.&archived=yes&id=22546
So what does RM stand for?
But the watch is not for the sea ...
Some more details from MF
https://www.iwc.com/member/forum/search_all.asp?table=archives&sMessage=italian&archived=yes&id=63486
For those wanting to know more, On Time, Italian Style by Friedrich Wagener and Thomas Konig in Watch International #1/2003 provides further detail.
Cheers from the cellar