Pretty much the only way to dive in Burma is on a liveaboard safari, and most of these depart from southern Thailand. Scuba diving in what is also called Myanmar is a fantastic experience, but logistics and distances to travel make it quite an adventure. There are hundreds of islands and countless locations which are (or could be) world-class diving sites. For several reasons, nearly all Myanmar diving liveaboards are based in Thailand. They take you across the border, process passports etc in the border town Kawthoung, and then off you go diving. But if you are already in Myanmar at the start of your trip, it's usually possible to join in Kawthoung.