M class are a very wide group, some of which had 3 funnels, and some had 3 propellers.
The R and S classes were more uniform in appearance, all having two funnels and two propellers. All were also about 276 feet long, while the M class varied in length (apart from looks, all depending on the builder, the Admiralty type had 3 funnels, for instance).
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Thank you Kim for the crest
"Never fear to try on something new. Remember that the Titanic was built by professionals, and the Ark by an amateur"