Net Entertainment created an online slot that incorporates the thrills of underwater warfare, in which submarines make use of a sonar system. Once an enemy vessel has been detected and confirmed, the submarine has to run silently so it could launch an attack and at the same time avoid detection. Players will experience the feel of being one of the submarine crew, as the online slot adds excitement to the process of unraveling the winning combinations and activating the Bonus Game, by using the mechanics of a sonar system.

To play this 5-reel online slot, live bets must be placed on all paylines; although the number of lines to bet on is adjustable in each level, starting from 25 up to 250. Bets can be adjusted as well and according to coin value from $/£0.01 to $/£0.50. This means wagers can be as low as $/£0.25 or as high as $/£125.

The Sonar Alarm icon serves as the WILD symbol that can take the place of other icons to form winning combinations. There are 14 of such icons but most stay hidden and can only be revealed by the ECHO Wild, a pulsating radar symbol that emerges only in reel 3.

The interactive ECHO Bonus Game can also be triggered by a pulsating radar symbol, but one that senses the presence of tiles with concealed Torpedo icons. There are five such tiles and each has an equivalent multiplier. The interactive bonus game provides a periscope view of five enemy ships in sight, with each ship having an equivalent number of coins. Winning bonus rewards entails firing on a chosen target, while the prize outcome depends on the number of coins and the torpedo multiplier, times the coin value when the bonus games was activated.