This study was conducted on Royal Malaysian Navy submariners who were having training in France. It was designed to compare the oral health experiences and practices while under water and on land. Methods Eightysix Royal Malaysian Navy (RMN) submariners, who had undergone at least one cycle (288 hours) of under water training, were selected to participate in a self-administered questionnaire survey. Results Seven percent of the respondents reported oro-facial pain and discomfort; 9.3% reported bleeding gums and 12.8% experienced halitosis while under water. Of those experience oral problems, 82% reported disruption of their daily activities while under water. The study showed that 82.5% of them brush their teeth at least twice a day and 94.2% rinse after meals when there were under water. Meanwhile studies on land showed that 90.7% of them brush their teeth at least twice a day and 96.5% rinse after meals. Flossing was not practiced by most of the respondents. Conclusion It is concluded that brushing and rinsing are practiced regularly by submariners regardless whether they are on land or under water but flossing is not a common practice both on land and under water. Dental emergencies, such as toothache, TMJ pain and discomfort do occur during submarine operations and disrupt their daily activities. This might poses a threat to submarine operations.