If you ever have to fire a gun in the Navy, you’re already deeply fucked.

I mean, I don't disagree with the broad point that it's unusual, but...

https://en.wikipedia.org/wiki/USS_Buckley

On 22 April 1944, she joined hunter-killer Task Group 21.11 (TG 21.11) for a sweep of the North Atlantic and Mediterranean convoy routes. The ship was west of Africa near the Cape Verde Islands in May.[1] In the early morning of 6 May, aircraft from the escort carrier Block Island (CVE-21) reported an enemy submarine approximately 20 miles from Buckley. The ship steamed toward the U-boat at full speed. Meanwhile, U-66 had exhausted supplies and surfaced to recharge batteries and waited for a supply ship. At 0308, believing the approaching ship was German, U-66 launched three flares. The distance between the two vessels was 4,000 yards when the U-boat realized the actual identity of the ship approaching them.[1]

U-66 fired a torpedo, which Buckley dodged. The sub fired machine guns at the destroyer escort which returned fire with three-inch guns hitting the submarine's forecastle. Buckley then unleashed all its weapons on their target, repeatedly striking the conning tower as the sub backed away and fired another torpedo, which the Buckley avoided.[1] At 0328 Buckley rammed the German submarine U-66 and the two vessels were briefly locked together. Some members of the German crew exited their burning boat, and hand-to-hand combat ensued using small arms and whatever weapons were at hand (such as coffee mugs and shell casings). The Buckley backed off, but the submarine pursued, striking the Buckley on the starboard side at the engine room. The collision also broke the ship's starboard propeller shaft.[1] The U-66 disengaged and slowly backed away, but not before hand grenades were thrown into the gaping hole in the flaming conning tower.[1] The submarine sank at 0341 in 17°17′N 32°24′W.

https://en.wikipedia.org/wiki/USS_Borie_(DD-215)

During her fourth patrol, Borie got a radar contact on U-256 shortly after 1943 hours, 31 October and closed in. The U-boat promptly crash-dived. Two depth charge attacks forced her back to the surface, but she again submerged; after a third attack, a large oil slick was observed. Though U-256 made it home badly damaged, Hutchins believed the target to be sunk, and signalled Card: "Scratch one pig boat; am searching for more."

Borie then got another radar contact about 26 miles (42 km) from the first, at 0153 hours on 1 November 1943, range 8,000 yards (7,300 m) and charged in to engage.[5] At 2,800 yards (2,600 m) radar contact was lost, but sonar picked up the enemy sub at about the same time. Borie engaged U-405 (a Type VIIC U-boat) hours before dawn, at 49°00' N., 31°14' W.[5] There were 15-foot (4.6 m) seas, with high winds and poor visibility. The destroyer initially launched depth charges, after which the submarine came (or was probably forced) to the surface. Borie then came about for another attack, engaging with 4-inch and 20 mm gunfire at a range of 400 yards (370 m).[5]

The sub's six 20mm autocannons scored hits in the forward engine room and several scattered and harmless hits near the bridge, and her deck gun crew traversed their 88 mm (3.5 in) gun and took aim for their first shot at Borie's waterline; but Borie's 20 mm gunfire killed every exposed member of the sub's crew topside, and a salvo of three 4-inch shells then blew off the sub's deck gun before it fired a round.[5] Borie then closed in and rammed U-405, but at the last moment, the submarine turned hard to port and a huge wave lifted the Borie's bow onto the foredeck of the U-boat.[4]

After the ramming, Borie was high-centered on top of U-405, and until they separated, exchanges of small arms fire took place. This was a unique battle: unlike most other modern naval battles, it was decided by ramming and small arms fire at close range. Borie's 24-inch spotlight kept the submarine illuminated throughout the following battle, except for brief periods when it was turned off for tactical reasons.

The two ships were initially almost perpendicular to one another; as the battle progressed, wave action and the efforts of both crews to dislodge from the enemy ship resulted in the two vessels becoming locked in a "V" for an extended fight, with the U-boat along Borie's port side. The two ships were locked together only 25–30° from parallel. The action of the seas began to open seams in Borie's hull forward and flood her forward engine room.[5] The submarine's hull, made of thicker steel and sturdier beams to withstand deep diving, was better able to handle the stress. Hutchins reported later, "We were impressed by the ruggedness and toughness of these boats."[6]

Normally, in a surface engagement, the superior armament, speed and reserve buoyancy of the destroyer would have been decisive. But in this unusual case, the destroyer was unable to depress her 4-inch and 3-inch deck guns enough to hit the sub, while all of the submarine's machine guns could be brought to bear. One or two 4-inch gun crews attempted to fire, but their shells passed harmlessly over the target. Borie's crew had a limited number of small arms, however, and the German deck mounts were completely open and had no protection. The executive officer had presented a virtually identical situation during drills on 27 October – a theoretical ramming by a U-boat on the port side – and as a result, after the ramming, Borie's crew took immediate action without orders.

In the extended and bitter fighting that ensued, several German sailors were killed in desperate attempts to man the submarine's deck weapons. As each man emerged from the hatch and ran toward the guns, he was illuminated by Borie's spotlight and met by a hail of gunfire. Borie's crew engaged the enemy with whatever was at hand: Tommy guns, rifles, pistols, shotguns intended for riot control, and even a Very pistol.[5] Borie's executive officer and a signalman fired from the bridge throughout the fight. One German sailor was hit in the chest with a Very flare. One of the Oerlikon 20 mm cannon was also able to fire.[5]

Borie's crewmen could clearly see a polar bear insignia painted on the conning tower and the three numerals of the submarine. The bow of the sub had been badly damaged by the depth charges and she was unable to submerge. U-405's deck armament was extensive: in addition to the 88 mm gun, she also had six Flak 38 autocannons, in one quadruple and four single mounts. These weapons would have been devastating to Borie's exposed crew if they had been continuously manned. Occasionally, a German crewman would reach one of the Flak mounts, and open fire briefly before he was killed. Other German sailors kept up a sporadic small arms fire of their own from open hatchways.[4]

There are also cases where Navy personnel have had to fight on land, like at Wake Island:

https://en.wikipedia.org/wiki/Battle_of_Wake_Island

Also present on the island were 68 U.S. Navy personnel.

Not the US Navy, but one important battle the US fought in the War of 1812 that I can think of off the top of my head had British forces at the Battle of New Orleans. This had a a significant set of unusual combatants on each side; the Americans had a bunch of militia and volunteers from the town who showed up, as well as a pirate and his forces, and the British made use of some Royal Navy sailors:

https://en.wikipedia.org/wiki/New_Orleans_British_order_of_battle

Naval Brigade of 100 sailors from the fleet, in combat, commanded by Rowland Money of HMS Trave,[31] who participated in the attack on the west bank of the Mississippi.[14][32][15] Casualties 8 January: Royal Navy casualties were two dead, Captain Rowland Money and 18 seamen wounded.[4]

You think they shoot rifles off that thing? Not even a little bit.

It happens.

Big ships will set up ranges where the backstop is the ocean, little ones throw buoy targets off the side and shoot them.

Like, it's not a daily thing, but if you're out to sea long enough it'll happen