Tank-Borne Machine Guns (Hull Mounted and Otherwise)

[bojan]

And their 107mm field gun was formally designated "42 line gun" originally.

[bojan]

1 hour ago, DKTanker said:

4.2" or 107mm mortar also falls into that obscure category.  Why 4.2" and not 4.25"?  The 107mm part is easy to explain, 4*25.4= about 107.  Or did 107mm proceed 4.2", and if so, why 107mm and not 105mm or 110mm?

107mm war a reasonably popular caliber in first half of 19th century, but fell by wayside by the second half in favor of 105mm, with only Russia keeping it in the field artillery.

Both US, British and Soviets had 4.2/107mm" mortars, so there mush be some connection of why 4.2 and not 4.25.

 

Edited March 4, 2022 by bojan

[sunday]

2 minutes ago, bojan said:

And their 107mm field gun was formally designated "42 line gun" originally.

42.12 line.

Then 132mm rocket would be 52 line

[bojan]

12 minutes ago, sunday said:

42.12 line.

Then 132mm rocket would be 52 line

No, 42. Their true caliber is 106.68mm

A lot of Russian/Soviet gun are really in old measures. Mind boggling, but there it is.

23mm is 22.86 - 9 lines

76mm is 76.2mm - 30 lines

107mm is 106.68mm - 42 lines,

122mm is 121.92 - 48 lines

152mm is 152.4 - 60 lines. Exception is 152mm 2A36 which is a "true" 152mm, not 152.4, as it did not need to be able to use legacy ammo.

203mm is 203.2mm - 80 lines

"True" metric ones were 37mm, 45mm, 85mm, 100mm, 115mm, 125mm.

I am not sure for 180mm naval or field guns.

Edited March 4, 2022 by bojan

[bojan]

12 hours ago, sunday said:

42.12 line.

Then 132mm rocket would be 52 line

That one was decided by the size of the propellant grain they could be make at the moment.

Edited March 5, 2022 by bojan

[sunday]

Add 130mm to the weird ones like the 180mm.

Or, perhaps that 180mm could be related to that 17cm German long range heavy cannon.

[Olof Larsson]

27 minutes ago, sunday said:

7.62mm is three lines (tenths of an inch) in the old Russian unit system

Yes, but they ar not true 3-lines i.e. .300, but a .303. So like a .303 brittish.

[DougRichards]

6 hours ago, sunday said:

4 inches are 101.6mm, one of the standard medium caliber of naval guns at the turn of the 20th century.

How 105mm came to be such a popular caliber is a kind of mystery for me, but the French finally went rational and began to manufacture 100mm naval guns. The Japanese had already done so in WWII with their excellent 100/65 type 98 gun. 

There are the German 12.8cm guns of WWII. Curiously, 5 inch equals 127mm. Probably there is some relation here.

8.8cm is another weird caliber.

8.8cm weird?  The Ordnance 25pdr was 87.6mm  (3.45 inches)

The different bores can be considered as a result of form follows function, or rather ballistic efficiency for a particular weight of projectile to be placed on target. Yes there is some history / tradition about it of course, but was it just coincidence that so many navies used 21" torpedoes in WW2?

Edited March 5, 2022 by DougRichards
foolishness

[sunday]

4 minutes ago, DougRichards said:

8.8cm weird?  The Ordnance 25pdr was 87.6mm  (2.45 inches)

That is a gun whose caliber is given in pounds. Enough to call it weird, also. 😋

[bojan]

1 hour ago, sunday said:

3.5" are equal to 88.9mm, yes, it could be the right explanation. Bazooka caliber also.

Inch was not standard, it varied across Europe, as demonstrated previously. Look at just German mess - inch could be 1/10, 1/11 or 1/12 of foot. And foot size varied widely:

https://en.wikipedia.org/wiki/Obsolete_German_units_of_measurement#Length

 

Than there is a fact that some gun derived their caliber from a mass of their projectile.

Edited March 4, 2022 by bojan

[R011]

4 hours ago, DKTanker said:

4.2" or 107mm mortar also falls into that obscure category.  Why 4.2" and not 4.25"?  The 107mm part is easy to explain, 4*25.4= about 107.  Or did 107mm proceed 4.2", and if so, why 107mm and not 105mm or 110mm?

Perhaps because 105 mm was in use for a different weapon and they wanted to avoid confusion? Are they actually 4.2 inch or are they really 105 mm or something?

[sunday]

2 minutes ago, R011 said:

Perhaps because 105 mm was in use for a different weapon and they wanted to avoid confusion? Are they actually 4.2 inch or are they really 105 mm or something?

Do you mean like calling the caliber of the 6-inchers using as land artillery as 155mm, or how the "77mm" gun in the Comet tank came to be?

[CaptLuke]

4 hours ago, 17thfabn said:

That one is easy! Because as a 4.2" it got the cool nick name the Four Deuce mortar.

The 4.2 inch mortar had to be one of the last weapons the U.S. adopted with inch versus millimeter designation?

You could have a Deuce and a Half bring up a load of Four Deuce ammunition. 

Stems from US Chemical Corps work to extend the range of their 4" Stokes mortars from WWI.  They did a series of experiments . . . 

Quote

from Chemical history: "M1 4.2-inch Chemical Mortar. In the early 1920s, Captain Lewis M. McBride experimented with rifling the barrel of the 4-inch Stokes Mortar. In truing the inside of the barrel preparatory to rifling, the bore became 4.2 inches in diameter. 

 

[shep854]

"The Ordnance 25pdr was 87.6mm  (2.45 inches)"--DougRichards

Err...you mean 3.45 inches??

[sunday]

15 minutes ago, shep854 said:

"The Ordnance 25pdr was 87.6mm  (2.45 inches)"--DougRichards

Err...you mean 3.45 inches??

Oops... Silly me did not check 😳

You are absolutely right, Shep

Doug, are mathematics different down under, or what? 🦘

A weird caliber, still.

Edited March 5, 2022 by sunday

[Coldsteel]

Budget cuts. I believe I've read what was wanted was something nearer 4 inches but 3.45" was the largest the bore of the 3.3" 18 pounder could be increased to safely, to enable the existing 18 pounders to be reused and save money.

[DougRichards]

1 hour ago, shep854 said:

"The Ordnance 25pdr was 87.6mm  (2.45 inches)"--DougRichards

Err...you mean 3.45 inches??

waking from sleep

[Poopstain]

5 hours ago, wendist said:

But not terribly impressive.

Ah, thread-drift.   Is there nothing it cannot do?  🤣

[sunday]

25 minutes ago, Poopstain said:

Ah, thread-drift.   Is there nothing it cannot do?  🤣

Of course there is - you could get used to it.

Edited March 5, 2022 by sunday

[bojan]

1 hour ago, R011 said:

Perhaps because 105 mm was in use for a different weapon and they wanted to avoid confusion? Are they actually 4.2 inch or are they really 105 mm or something?

AFAIK all 3 were actual 4.2". US one was rifled, Soviet was smoothbore (being just middle between their 82mm and 120mm), IDK for British.

Which reminded me - 120mm, there are both metric and inch pattern of this caliber. 120mm mortar is metric, but there were 120mm naval guns (Russian at least) that were actually 47 line/4.7 inch.

Edited March 5, 2022 by bojan

[usernamedeleted]

1 hour ago, bojan said:

 

Which reminded me - 120mm, there are both metric and inch pattern of this caliber. 120mm mortar is metric, but there were 120mm naval guns (Russian at least) that were actually 47 line/4.7 inch.

They were probably all "truly" 120mm. QF 4.7in guns had been very popular in the 1890s, many built by Elswick. Their true bore diameter was 120mm, about 4.724in. Russia imported a Canet gun design a few years after the "4.7in" took off, and I think it too was exactly 12cm. Later imported 4.7in Vickers guns, which almost assuredly were 120mm, as all British "4.7in" weapons were.

Rewinding a bit to the original topic, is there much known on why the IS-7 had so many fixed MGs?

[Interlinked]

1 hour ago, usernamedeleted said:

Rewinding a bit to the original topic, is there much known on why the IS-7 had so many fixed MGs?

I haven't read much about the IS-7, but I'd assume it was the same reason why the IS-2 had a front-facing fixed bow machine gun and a manned rear-facing machine gun, just adapted for the limitations of external mounts. The two pointing for the rear would presumably be to deter enemy infantry from approaching the tank from the rear or climbing up on the engine deck to blow it up (same as the KV-1 and IS, IS-2, and some Japanese tanks), and the ones pointing to the front would serve the same purpose as any hull machine gun. Having two of each is not necessarily overkill, but rather a means to provide redundancy in case one jams, and to provide enough ammo and density of fire to compensate for the machine guns being fixed and not reloadable in the middle of combat. 

I think a good example that shows their belief that "2 external machine guns = 1 internal machine gun" is the T-54, because that originally had two external fixed forward-firing machine guns, but that was replaced by a single internal fixed bow machine gun. Conversely, the Strv 103 had two external fixed machine guns too, but those fired alternately, one at a time, which also makes sense because the Strv 103 could be aimed so it just needed to conserve ammo and two guns for redundancy.

All that said, even though this all makes sense and everything seems to be tied up neatly, I don't know what the designers specifically intended. It's so hard to find any writings or documentation about a topic so mundane as fixed machine guns. 

[bojan]

4 hours ago, usernamedeleted said:

...Rewinding a bit to the original topic, is there much known on why the IS-7 had so many fixed MGs?

Idea of defense vs invantry, especially in urban environment. MGs are cheap, heavy tanks are expensive and most of those were externally mounted so did not waste space inside..

 

  

4 hours ago, usernamedeleted said:

They were probably all "truly" 120mm. ...

Thank you for that data.

Edited March 5, 2022 by bojan

[Rick]

7 hours ago, sunday said:

Of course there is - you could get used to it.

A most true statement, and some interesting pearls of information have come out of drifting threads. The most classic was the one from tanks to dog flatulence in just a few posts while actually making, somewhat of course, some, uhmmm, scents.  

[Rick]

6 hours ago, bojan said:

AFAIK all 3 were actual 4.2". US one was rifled, Soviet was smoothbore (being just middle between their 82mm and 120mm), IDK for British.

Which reminded me - 120mm, there are both metric and inch pattern of this caliber. 120mm mortar is metric, but there were 120mm naval guns (Russian at least) that were actually 47 line/4.7 inch.

Have always been impressed by the variety of naval guns through the ages between 100mm through 130mm.