Never send a CV/Resume without a covering letter, this includes emails. The covering letter is an essential part of the Resume and should not be neglected.
Keep the covering letter short and completely to the point, do not mention too much in this letter that you have already stated in the CV, if you write it by hand ensure that it is neat and legible, and use good quality paper, blue ink is better than black and a fountain pen better than ball-point. Remember that the person who you are writing this letter to knows NOTHING about you except what is written in the letter and the CV, always write the letter to a name e.g. Mr. Smith, if you do not know the name – find out. As a last resort you can send it to a title e.g. Personnel Manager but always try to obtain a name.
An example of a covering letter might go as follows:
Dear Mr. Smith
I understand from an advertisement that your company has in Yellow Pages that you undertake Close Protection work. I have recently completed a contract overseas (I have recently completed a comprehensive course in Close Protection with) and am now actively seeking another (my first) assignment. I have enclosed a CV which outlines the experience etc, etc. I look forward to hearing from you soon