Since they started patrolling in 1957, they have gone under the ice and measured with their radar looking upwards to measure how thick it is because they can only surface in areas where it's three and a half feet thick or less.
ตั้งแต่เริ่มลาดตระเวณในปี 1957 ล่องไปภายใต้น้ําแข็ง แล้วส่งเรดาร์ตรวจวัดขึ้นไป