HK54: The original model that was produced in 1964.
The 54 designation is from the Heckler & Koch company's old system that indicates that it is a submachine gun/assault carbine (5-) chambered for the 9×19mm cartridge (-4).
It had a charcoal-gray phosphated finish rather than the matte-black lacquered finish used on later models and had narrow slotted metal handguards.
Its major differences were that it had a longer and heavier bolt carrier than the MP5 and a flip up "ladder"-style rear sight (like the early G3 rifle) rather than the MP5's aperture sight.
Its original 15- or 30-round steel magazines were straight rather than curved, had a plastic follower, and were reinforced with ribs (thus their nickname of "waffle"-type magazines).

MP5: A slightly modified version of the HK54 first created in 1966.
A matte-black lacquered finish instead of the grayish phosphated finish was introduced for export models in 1977.
It originally had the narrow checkered metal "Slimline" handguards in the place of the HK54's narrow slotted metal ones.
These were later replaced by the thicker "Tropical" handguards in 1978.
The proprietary Heckler & Koch "claw mount" rails for mounting optical and electronic scopes were added around 1973.
The improved 15- and 30-round magazines were adopted in 1977; they were curved, had unribbed sides, and had chromed-steel followers.

MP5A1: No buttstock (endplate/receiver cap in place of buttstock), "SEF" trigger group.

MP5A2: Fixed buttstock, "SEF" trigger group.

MP5SFA2: Fixed buttstock, single-fire (SE) trigger group.

MP5A3: Retractable buttstock,"SEF" trigger group.

MP5SFA3: Semi-automatic carbine version of MP5A3.
Retractable buttstock and single-fire (SE) trigger group.

MP5A4: Fixed buttstock, 3-round burst trigger group.

MP5A5: Retractable buttstock, 3-round burst trigger group.

MP5-N: Model developed specifically for the U.S. Navy.
Ambidextrous "Navy" trigger group, 3-lug/threaded barrel for attaching a sound suppressor; rubber-padded retractable stock.

MP5F: Model developed in 1999 specifically for the French military.
Rubber-padded retractable stock, ambidextrous sling loops/bolts and internal modifications to handle high-pressure ammunition.

MP5K: Short (kurz) version created in 1976.
It has a shortened 4.5 in (114 mm) barrel, shorter trigger group frame, and a vertical foregrip rather than a handguard.
There are no MP5KA2 or MP5KA3 models because it does not come with a fixed or retractable stock.

MP5K Prototype: A stockless, cut-down MP5A2 with regular iron sights and an open vertical foregrip.
It was created in 1976.

MP5KA1: MP5K with smooth upper surface and small low-profile iron sights; "SEF" trigger group.

MP5KA4: MP5K with regular iron sights; four-position 3-round burst trigger group.

MP5KA5: MP5K with smooth upper surface and small low-profile iron sights; four-position 3-round burst trigger group.

MP5K-N: MP5K with "Navy" trigger group and 3-lug/threaded barrel for mounting suppressors or other muzzle attachments.

MP5K-PDW: Personal Defense Weapon; MP5K-N variant introduced in 1991 for issue to special operations aircraft or vehicle crews.
It adds a Choate side-folding stock, 5-inch 3-lug barrel for mounting a quick-detachable Qual-A-Tec suppressor, and an ambidextrous 4-position trigger group with a 3-round burst mode.
A shoulder cross-draw or thigh quick-draw holster is available.

MP5SD: An MP5 model with an integrated suppressor (Schalldämpfer) created in 1974.

MP5SD1: No buttstock (endplate/receiver cap in place of buttstock), "SEF" trigger group, integrated suppressor
MP5SD2: Fixed buttstock, "SEF" trigger group, integrated suppressor.

MP5SD3: Retractable buttstock, "SEF" trigger group, integrated suppressor.

MP5SD4: No buttstock (endplate/receiver cap in place of buttstock), 3-round burst trigger group, integrated suppressor.

MP5SD5: Fixed buttstock, 3-round burst trigger group, integrated suppressor.

MP5SD6: Retractable buttstock, 3-round burst trigger group, integrated suppressor.

MP5SD-N1: Fixed buttstock, "Navy" trigger group, KAC stainless steel suppressor.

MP5SD-N2: Retract
HK54: The original model that was produced in 1964. The 54 designation is from the Heckler & Koch company's old system that indicates that it is a submachine gun/assault carbine (5-) chambered for the 9×19mm cartridge (-4). It had a charcoal-gray phosphated finish rather than the matte-black lacquered finish used on later models and had narrow slotted metal handguards. Its major differences were that it had a longer and heavier bolt carrier than the MP5 and a flip up "ladder"-style rear sight (like the early G3 rifle) rather than the MP5's aperture sight. Its original 15- or 30-round steel magazines were straight rather than curved, had a plastic follower, and were reinforced with ribs (thus their nickname of "waffle"-type magazines).
MP5: A slightly modified version of the HK54 first created in 1966. A matte-black lacquered finish instead of the grayish phosphated finish was introduced for export models in 1977. It originally had the narrow checkered metal "Slimline" handguards in the place of the HK54's narrow slotted metal ones. These were later replaced by the thicker "Tropical" handguards in 1978. The proprietary Heckler & Koch "claw mount" rails for mounting optical and electronic scopes were added around 1973. The improved 15- and 30-round magazines were adopted in 1977; they were curved, had unribbed sides, and had chromed-steel followers.
MP5A1: No buttstock (endplate/receiver cap in place of buttstock), "SEF" trigger group.
MP5A2: Fixed buttstock, "SEF" trigger group.
MP5SFA2: Fixed buttstock, single-fire (SE) trigger group.
MP5A3: Retractable buttstock,"SEF" trigger group.
MP5SFA3: Semi-automatic carbine version of MP5A3. Retractable buttstock and single-fire (SE) trigger group.
MP5A4: Fixed buttstock, 3-round burst trigger group.
MP5A5: Retractable buttstock, 3-round burst trigger group.
MP5-N: Model developed specifically for the U.S. Navy. Ambidextrous "Navy" trigger group, 3-lug/threaded barrel for attaching a sound suppressor; rubber-padded retractable stock.
MP5F: Model developed in 1999 specifically for the French military. Rubber-padded retractable stock, ambidextrous sling loops/bolts and internal modifications to handle high-pressure ammunition.
MP5K: Short (kurz) version created in 1976. It has a shortened 4.5 in (114 mm) barrel, shorter trigger group frame, and a vertical foregrip rather than a handguard. There are no MP5KA2 or MP5KA3 models because it does not come with a fixed or retractable stock.
MP5K Prototype: A stockless, cut-down MP5A2 with regular iron sights and an open vertical foregrip. It was created in 1976.
MP5KA1: MP5K with smooth upper surface and small low-profile iron sights; "SEF" trigger group.
MP5KA4: MP5K with regular iron sights; four-position 3-round burst trigger group.
MP5KA5: MP5K with smooth upper surface and small low-profile iron sights; four-position 3-round burst trigger group.
MP5K-N: MP5K with "Navy" trigger group and 3-lug/threaded barrel for mounting suppressors or other muzzle attachments.
MP5K-PDW: Personal Defense Weapon; MP5K-N variant introduced in 1991 for issue to special operations aircraft or vehicle crews. It adds a Choate side-folding stock, 5-inch 3-lug barrel for mounting a quick-detachable Qual-A-Tec suppressor, and an ambidextrous 4-position trigger group with a 3-round burst mode. A shoulder cross-draw or thigh quick-draw holster is available.
MP5SD: An MP5 model with an integrated suppressor (Schalldämpfer) created in 1974.
MP5SD1: No buttstock (endplate/receiver cap in place of buttstock), "SEF" trigger group, integrated suppressor
MP5SD2: Fixed buttstock, "SEF" trigger group, integrated suppressor.
MP5SD3: Retractable buttstock, "SEF" trigger group, integrated suppressor.
MP5SD4: No buttstock (endplate/receiver cap in place of buttstock), 3-round burst trigger group, integrated suppressor.
MP5SD5: Fixed buttstock, 3-round burst trigger group, integrated suppressor.
MP5SD6: Retractable buttstock, 3-round burst trigger group, integrated suppressor.
MP5SD-N1: Fixed buttstock, "Navy" trigger group, KAC stainless steel suppressor.
MP5SD-N2: Retract
Heckler & Koch MP5