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Peak vs Mean

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Previously, I discussed in detail what Soviet rate of fire tests actually measured. Long story short, the difference between the peak rate of fire (loading from the ready racks) and the average rate of fire (loading from all racks) was quite pronounced. Soviet figures reflected the latter scenario, which is why their rates of fire seem significantly slower when ROF figures are compared as is.

Let's take a look at another example: the Firefly, specifically the Sherman Ic. I've seen all sorts of figures on its rate of fire, from ten to twenty (!) rounds per minute. British tests, on the other hand, tell a different story.

The "Firefly" Shermans, Vc and Ic, had two ready racks on the turret basket floor: 2 rounds and 3 rounds. Loading and firing these rounds took about a minute. A very lengthy reload process followed. For starters, the loader had to empty the spent casings from the bag under the breech, since it was impossible to lift any more rounds up in the cramped space. If he was lucky enough to have a pistol port that wasn't welded up, chucking the cases through there was a little bit faster. British trials don't specify how long this took, but it would certainly add a lengthy chunk of time to the reload process.


These results are for the Sherman Vc, but the Ic had a nearly identical layout: five shells in ready racks, the rest in extremely inconvenient locations. 

Sherman Ic fighting compartment layout. Ammunition racks are highlighted in red.

You can see why it might take several minutes to extract the ammunition. Trials of the Sherman Ic have more precise information on how long it takes to take it out of the racks.


The left hand bins (8 rounds each) are pretty quick, especially if the turret is positioned favourably and the driver can help out. The downside is that he can't drive, so that makes the tank vulnerable if it's spotted. When loading from the racks underneath the turret basket floor (which contain nearly all the ammunition carried in the tank), the turret had to be lined up precisely, which made reloading even slower. Finally, the two bins that take the longest to access (2 and 3 minutes) contained more than half of the tank's ammunition, meaning that the rate of fire would drop significantly as the battle continued.

Shuffling ammunition from the less accessible bins to the more accessible bins also took a large amount of time, as no more than 5 rounds could fit on the floor at any given time. 

As you can see, while the peak rate of fire might be recorded as 5 RPM, the actual sustained rate of fire is a lot lower than that. Even loading from the most convenient rack, it will be a whole minute before the tank can fire again. From other trials I've posted, throwing out spent brass can take 2.4 seconds (Tiger II) to 2.9 (IS-2) seconds per casing. Even if you assume that the lighter 17-pounder casings take 2 seconds each to dispose of, that's another 10 seconds tacked onto the reloading process. Therefore, firing 10 times will take 3 minutes and 10 seconds, one shot per 19 seconds, or a hair over 3 rounds per minute. To compare, the SU-152 could fire off 10 rounds in its ready rack at a rate of fire of 2.8 RPM. 

When it came to the Germans, they didn't even have to expend their ready racks to experience a drastic drop in rate of fire. For example, British trials of the Tiger showed that picking out the last shells from the ready racks could take as much as 30 seconds apiece.

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