Table 1 of Uniform Crime Reports for 2011 shows the United States has a reported to police rape rate of 42.8/100,000 rapes. The 2010 National Crime Victimization Survey shows 188,380 rapes in the U.S.; the U.S. population in 2010 was 308 million. That gives 61.16 rapes per 100,000 population, our about 43% of the British Crime Survey victimization rate.
I certainly will not claim the United Kingdom has more than twice the rape rate because American women are allowed to own guns while British women for practical purposes are not, but it does make you wonder, doesn't it?
UPDATE: A reader says that the British Crime Survey figure that RapeCrisis uses is, not contrary to their claim, a count of rapes, but all sexual assaults (which would include unwanted touching of a sexual nature). I don't find that claim implausible, because groups that call themselves whateverCrisis are not generally terribly objective, but RapeCrisis make a clear distinction between sexual assaults in general and rape in particular:
Around 400,000 women are sexually assaulted and 80,000 women are raped each year (British Crime Survey).Worse, the reader who makes this claim cites a document that does not seem to support his claim.