A rundown of Navy commando frogman varieties:
1) Combat Swimmers: Killed James Bond and Lionel Crabb with underwater assault rifles, dolphins, underwater tanks, and ROVs. This is less a actual organization and more just a job some divers units are expected to do, though. The real purpose of the tanks and ROVs is mostly maintenance of harbor defenses, but there are weapons for them in case the enemy attacks through the sea in force, or the Maintenance Divers just don't have much use for them at the time. They can also do clearance diving, confusingly, and do that job as well, but their main job is machine gunning people who would try to plant limpet mines on ships or take sneaky pictures of sonars. Their second main job is swimming into harbors, cutting the defenses, machine gunning the defenders, and planting limpet mines on ships. Sort of a combination of PDSS and SEALs, with a maximum emphasis on seaborne sabotage and brief (minutes) forays onto piers and harbors or other near-shore targets to destroy something vital. Combat Swimmer Teams have the largest platoons of all frogmen units (24-men) excluding the Coastal Rangers, who are barely frogmen, and basically landmen. They are trained to be employed in either platoon or company strength, and companies often include delivery vehicle teams who are trained to use the Marke 9 Swimmer Delivery Vehicle, which is less a swimmer vehicle and more a underwater jeep that transports nuclear demolition bombs and captive carried mines to enemy harbors and up rivers.
2) Scout/Attack Divers: He.
Joined at the hip to the mission of hydrographic-beach zone reconnaissance and obstacle marking. To a lesser extent they can blow up obstacles, but they aren't world class EOD experts with at dozen sea mines memorized, they just know how to plant satchel charges and not to wave big metal sticks at the magnetic mine poles. Since beaches are also on the land, though, they tend to cross them and take pictures or sketches of pillboxes, artillery batteries, and whatnot. Their main job is generally reconnaissance, but they can also attack things, to the extent that an M72 LAW, a few 5.56mm magazines, a satchel charge, and some hand grenades per man can attack anything. Their preferred weapon for raiding is the naval fighter-bomber and the VHF radio, which this one is wearing, along with a few self defense items. If they aren't fighting they're usually drawing pictures in notebooks or blowing something up, like concrete bunkers or post obstacles. There are several teams, each specialize in certain environmental regimes, and this commando is dressed for a mid-latitude temperate climate.
Basically 1960s UDTs + some '80s SEAL stuff.
3) Maintenance Diver: Like a clearance swimmer, but for deep water. They maintain SOSUS networks, undersea fiber trunks, and sabotage them, as well as fight in the deep (>200 meters) ocean. They use atmospheric diving suits, deep submergence submersibles, and ordinary brass helmet and ROVs to do that job. Their main jobs are fixing, repairing, and maintaining things on or near the seafloor or near harbors. They can also perform salvage. Unlike the clearance swimmers, these guys are actual clearance divers. They've never even seen an underwater machine gun, but they can weld great underwater trusses and salvage anything. They're general purpose underwater engineers.
4) Mine/Demolitions Diver: Knows every sea mine, most obstacles, dams, and undersea infrastructures, and how to blow them up. Lives for exploding things underwater, works to keep them from exploding in the first place. Basically EOD divers who occasionally blow up fence posts or something. They like jumping from helicopters and live on minesweepers.
5) Coastal Rangers: They act like they know how to swim but they really don't. They can use a UBA and might be able to fight off an angry goldfish, but they're not really trained in combat swimming so much as they're trained in fighting in forests, jungles, and cities, and blowing up things like warehouses and liberating prisoners. 1960s SEALs, more or less. They're hard dudes who operating in 40+ man teams with 120mm mortars and Hellfire missiles manpacked across islets. They are landmen who pretend to be sailors. They're also the biggest Naval Commando unit. Platoons are still 16-men so they can fit inside a fast insertion craft.
His official name is "Scout/Raider Swimmer" which is abbreviated to S/A-Dyk.
He is dressed for a over-the-beach reconnaissance of moderate duration, less than 30 days, and probably carrying equipment for a little less than 15 days. He has a rucksack with a garbage bag lining for waterproofing which carries his utility/combat uniform, patrol cap, some food, and a waterproof radio, a smaller kit bag trailing that which carries his combat boots, socks, and other things like a toothbrush or chewing gum, and camouflage grease paint. Strung along the side of his rucksack is a long neoprene tube holding a 66mm anti-tank rocket and spare oxygen bottle, and additional magazines of ammunition are carried in the rucksack. Brown leather workman's gloves are also worn, although the Navy provides some trashy black leather gloves that are also OK, they also have separate wool liners and are a bit too big when worn without them. The new Boots, Combat, Leather, Brown are also worn, which incorporate a infrared suppressed, non-shine boot polish. Paratrooper-style (front plate only) "Halfback" body armor is worn, with a ballistic insert, and atop this is the standard webbing.
During the swim, he wears a Navy Mark 21 closed-circuit rebreather (sort of a combination of a LAR V and a couple other Draegers), a Navy Mark 7 wetsuit with a hood (technically good down to 48 F, but he would be wearing a drysuit in that sort of weather, so the water is moderately warm or chill, not cold), swim fins, and has a rifle slung over his back and exposed, although usually a condom or something is applied over the barrel and the bolt locked prior to lockout from the submarine. A field pack on his patrol belt might carry anti-personnel mines or demolition charges for destroying anti-landing obstacles, small bridges, and the like. The preferred explosive is the m/1118 demolition charge, which is composed of flexible strips of C4 and designed for cutting through steel posts and concrete, although bigger obstacles will generally require more substantial demolitions equipment. Standard webbing is worn, unzipped, so that the rebreather can be worn with the buckles fastened around his torso, and quickly doffed.
Around his left thigh he carries a waterproof bag holding field glasses, a teleoptic sight, and perhaps some night-vision goggles. The other thigh holds a Navy Mark 1 Mod 1 Underwater Pistol, which is a .17/38 caliber, six-shot, break action revolver that weighs approximately 3.25 lbs loaded. His ankle has a Navy Mod 4 Dive Knife which has a 5" blade with a serrated edge, wire cutter/stripper, and a smooth edge, for general purpose cutting of fishing lines, harbor nets, and throats. The oxygen bottle provides him with sufficient O2 for a comfortable 5 hours (or more) underwater, depending on the dive and speed. He can be expected to cover about a mile an hour, give or take a bit, with this equipment.
Once he has crossed over the surf zone to the tidal zone, preferably at night, he will remove his wetsuit and rebreather and bury them in the sand, making note of the location for later. Generally this landing spot is used as an orientation point and marked on a map. Donning his fatigues and applying camouflage paint to his face, neck, and arms, he resembles more a landman than a sailor at this point.
On shore he will likely recon the immediate beach, beginning by checking for obvious signs of obstacle placement (minefields), noting tides, and marking hydrographic features which are relevant for LSTs and other landing craft. Although not as much a risk as it once was, given the development of the amphibious tractor and the hovercraft, amphibious landings are still mired easily by command and magnetically detonated land- and sea mines. Additionally, shore defenses are important to monitor, although they are not quite literal pillboxes, and his job as such resembles that more of a long-range reconnaissance patrol than anything. Observation posts are used to monitor enemy troop movements near the beach (within 15 miles or so) and land mines and bazookas are used to defend the OPs in case of discovery by enemy troops or collaborating civilians. If discovered by civilians, the written SOP is to execute them immediately, as quietly as possible, and dispose of the body far enough away from the beach to draw attention away from the recon team, or preferably to distract the enemy by drawing his attention to a false landing area. Sometimes the body is simply thrown off a cliff and found a few days later when it washes up on a beach a couple miles away. Road and bridge reconnaissance is also important, and discerning the maximum load capacity of bridges near the beach zone is relevant for the Royal Marines, who are broadly mechanized, and rely on main battle tanks and tracked carriers.
During this initial reconnaissance phase of the assault, the enemy should not be sure if it is actually going to be attacked, and should be mostly unaware of the impending amphibious invasion. The information of the reconnaissance team is transmitted by wireless, encrypted, and generally in the form of data packets produced by the recon team's personal field computer, which allows them to send photographs and maps to Fleet planners.
After a couple of weeks, the reconnaissance troops dismantle their observation posts, hopefully haven't been discovered, and any corpses they've produced have ideally been disposed of in a manner which leaves the enemy confused, and return to their initial landing zone. They replace the O2 bottles in their rebreathers with the spares, the soda lime canisters are removed from their storage bags and replaced in the rebreather, fatigues are doffed and rucksacks packed to be watertight, wetsuits are donned, followed by the rest of the UBA gear, and the scout swimmers reenter the water to rendezvous with their extraction vehicle a few miles off the coast, which is typically a submarine but also sometimes a patrol boat or a Fulton equipped aircraft.
If rubber raiding craft are used during the initial insertion then the process is the same, except all equipment relevant to swimming is now a boat with an outboard motor that's been stewing in low tide for a fortnight.
Alternatively they can stick around with a brief resupply and direct air attacks in support of the landing force.
Divers like him are born two at a time from the 21" torpedo tube. Ordinary operation method is loading half the torpedo tubes at a time on a Fox-class [688i-expy] SSN with SDVs and the other half with the swimmers for each. Two swimmers can exit at a time from either tube. The Wolf-class [21-expy] SSN's 26" torpedo tube is large enough to accommodate a pair of swimmers laying down in a single chariot, and when flooded the swimmers can exit the tube through the torpedo's own propulsion system. The chariot torpedo allows commando frogmen to be delivered from up to 8 miles distant from a shore, although this assumes the frogmen swim the last third or so of that after anchoring their chariots to the seafloor, or hiding them inside a reef or wreck, or something. If the SSN can close to less than four miles distant from the shore, it can be expected that the frogmen do not require any SDVs to reach the beach and can perform the swim with rebreathers alone.
Generally, any SSN is expected to deliver all its swimmers in a single "volley", which precludes a Fox-class submarine from employing tube launched SDVs except for the smallest possible commando unit (a 4-man section), due to the limited number of torpedo tubes available. The Wolf class submarine can deploy a full platoon of commandos (16-men) from all tubes, either as swimmers or riding chariots. Although the Wolf class has an automatic loading system, the 26" tubes require use of the manual block & tackle when uploading swimmers and their torpedo, which while significantly slower than the automatic loader, is also quieter in operation.
All of these methods, except for the swim-out via manned torpedo, require some time spent by combat swimmers and sailors from the submarine in preparation and deployment of additional equipment from the torpedo tubes, functionally using them as lockout trunks. Claustrophobes need not apply!
Alternative methods of swimmer delivery include the use of dry deck shelters, attached to the escape hatch of the submarine, which act as a submersible hangar and allow all SSNs to deliver a single squad (8-men) of commandos in a wet environment. Although the mini submarine SDV "only" has an operating range of about 20 nautical miles, it can deliver combat swimmers almost as close to shore or harbors as manned torpedoes, and is significantly less taxing on their oxygen supplies as they can use onboard oxygen.
More advanced submersibles can be deployed in lieu of the dry deck shelter's streamlined storage, although these are larger, longer, and thus noisier for the submarine to carry, they have the benefit of carrying up to a single 16-man platoon plus two operators, and have a range of over 50 nmi with a cruise speed approaching 5 kts in good current, and 8 kts sprint.
Attack divers and combat swimmers also have access to a pair of special purpose, 1,800 ton diesel submarines, built using the propulsion systems of the latest diesel hunter-killers of the Royal Navy [similar to Soryu SSK but more teardrop shaped, and extremely automated] and a large SDV bay capable of holding two submersibles up to 18 meters in length. While the intended "high speed swimmer delivery vehicle" (turbine powered, using gaseous oxygen, with a 8-12 kts cruise speed) never materialized, the "swimmer platoon delivery vehicle" (essentially S401 or ASDS-but-not-badly-designed) appeared instead. Additionally, the diesel submarines can deploy swimmers through a pair of 26" torpedo tubes. The minisub hangar can be operated wet or dry, depending on the type of submersible.
Due to the limited nature of the SOF delivery submarines, although they are under direct control of the Naval Commando Branch, they are in high demand, and the most "ordinary" method of swimmer delivery is probably lockout through torpedo tubes near a beach to be reconnoitered or a harbor to be sabotaged (within 4-5 nautical miles), or through a submersible piggybacking on the SSN. Combat swimmers are the most frequent users of the diesel submarines' unique abilities, due to their preference for raiding in mass (>platoon strength) and need to conduct long-range (>20 miles) underwater operations to destroy deep waterway targets, such as canals, dams, nuclear powerplant cooling vents, and submarine bases with ADMs. By extension, coastal rangers prefer the rubber raider boat or the patrol craft, and the scout/raider swimmers prefer torpedo tubes or high altitude gliding-parachute jump.