A diver since 1969, Leslie was a diving officer for BSAC Special Branch in Singapore, and had held numerous positions with diving related non-profit groups. His research into diving history has been translated and published in numerous countries where he has also lectured. As a consultant, Leslie has worked for the National Geographic Society, the B.B.C., the US Navy, the History Channel and other companies. Non-profit fund raising programs introduced and overseen by Leslie have raised over a million dollars and he has contributed thousands of volunteer hours to diving non-profit causes. Leslie is the North American representative of pioneer divers Hans and Lotte Hass, is the recipient of numerous awards and, by the personal sponsorship of Dr. Christian Lambertsen, is a Lifetime Member of the UDT/SEAL Association.