Thanks for your help everyone. Yes, the morse key is a switch which toggles the serial control lines.... the software recognises this and acts accordingly. The CTS, DSR etc. lines are not being used in their "proper" sense and no serial data (as such) flows down the data lines. I was hoping I could send these fake control commands from my UNO via the virtual COM port (that is Arduino connected to my PC via USB) and therefore send morse to CWCOM directly. This is part of a project to read morse from a radio receiver sending audio into one of the analogue-in's on the UNO. From your comments, it seems that sending RTS, DSR etc. is a non-starter. I shall look into a USB/serial converter and check out voltage compatibility with the RS232 standard. Cheers again for your help!
All the best
Paul