H.D Rumjahn was an outstanding doubles specialist, and teamed up with his cousin, S.A. Rumjahn, to capture five Hong Kong National Grass Court Championships between 1927 and 1940, and was also a finalist in 1938 and 1941. Although competing predominantly in doubles, he did experience some success in singles, capturing the Championships in 1937, and finishing runner-up in 1936 and 1938.