The best way to reach Havelock is by the air conditioned catamaran ferry, which takes only 90 minutes from Port Blair. There are government ferry services available as well which take about 2.5 hours. Do book your tickets in advance during peak season.
You can fly to Havelock from Port Blair in 20 minutes in a seaplane operated by Pawan Hans Helicopters Limited. The services are usually available on Mondays, Wednesdays, Thursdays and Saturdays.