Navy's New Swimmer-Smacking Grenade

A while back, someone noticed that a vast number of US assets -- from ships to pipelines and port facilities -- were vulnerable to attack by divers. DANGER ROOM has looked at a whole range of concepts for dealing with them, from underwater acoustic weaponsto (alleged) killer dolphins -- not to mention scuba-diving guards armed with exotic underwater firearms, or bang sticksor even shark darts. But the basic technique for tackling hostile divers has not changed much over the years: you toss in a grenade.

Shockwaves propagate much more effectively through water than through air, so blast can stun or kill at much greater ranges. But someone decided it was time for an upgrade.

The Navy recently put out this press release describing their new Anti-Swimmer Grenade, which will replace the obsolete Mk3A2 concussion grenades previously used for this role:

“The MK3 grenades currently being used,” Gabriel Soto explained, “are not very effective. They only have a four-to-five-second delay before detonation, which means they don’t get very deep.” And they can pose a threat to the user as well, he said.
Since they do not have built-in safe-arm features, once the pin is pulled and the lever released, they detonate in four to five seconds.

*The ASG meets the basic requirements in the Coast Guard memorandum—and then some. The user sets its detonation depth in 10-foot increments from 10 to 100 feet, and it uses state-of-the-art missile safe-arm technology that won’t allow it to detonate unless certain criteria are met. *

*The ASG uses battery power and a sequence of fail-safe checks of timers and a depth pressure sensor to fire an exploding foil initiator that initiates a booster and main charge. Before the actuating pin is pulled, the fuze power inputs are physically disconnected from the battery terminals and shorted together. The pin cannot be pulled until the operator rotates the detonation depth dial. Once the pin is pulled, the ASG must sense that it is in a water-pressure environment before it will fire. If it does not sense this environment after a certain period of time, it will render itself safe. *

*… The ASG also packs three times the explosive mass of the MK3A2.
Preliminary testing indicated that it significantly extends the effective depth and range. The project has passed an initial “own-boat”
hazard test in which a main charge was detonated underwater at the minimum safe-separation depth.
*

**Meanwhile, Ares
reports that Rheinmetall are working on their portable depth charge, which comes in two flavors: an 800g 'signal' grenade and a 1.4 kg killer version.

Back in the old days, they did not rely on fancy technology for this job, just a lot of explosive. Sometimes an unbelievable amount, as this account
(complete with photos) of life on a floating base in Vietnam recalls.
The threat from saboteurs known as 'swimmer zappers' planting explosives meant that extreme measures were needed:

*The floating logs and mooring buoy were part of an anti Vietnam sapper/swimmer razor wire net that we designed to discourage the VC
"indians" from swimming in and planting charges. They still tried six times…all unsuccessfully. However, the CIA guys brought a VC "chu how"
guy over one day and he described a successful "dry run" he had done.
We "prophilacitcally" threw quarter-pound pound TNT depth charges in the water from two ends of the base at a random rate of about ten per hour. *

Needless to say there were not too many fishes around….
We went through about ten thousand depth charges each month. I went to sleep listening to the comforting sound of explosions.