Mr. Gardner posted:
On the naval bombardment, your math is off. The four cruisers firing 60 rounds per
gun amounts to just 332.4 tons in about 30 minutes of fire (277 lbs per shell, x 60 rpg x
10 guns per cruiser x 4 cruisers).
I am going to do some math here.
First, the IJN CAs carried 120 shells per gun. ( 1200 per CA as NORMAL STOWAGE - they could carry more.
The firing cycle for the 20 cm 50 caliber was 12-15 seconds as close range, 20-30 seconds at long range.
It is likely that the Suzuyas would engage the islands at about 15,000 yards, so the firing cycle is about
20 seconds, or three rounds per minute.
Which means they would empty their guns in about 40 minutes firing at rapid fire rate. But, if they
took their time, and did a proper job of it, they could spend two hours firing all 1200 from each
The weight of the Japanese 20 cm AP shell was 277 lbs. The HE shell was lighter - I have seen figures
of 253 lbs, 225 lbs, and 200 lbs, from different sources. I chose to use the lightest figure, to give the
IJN the least advantage.
So, here's the Math:
4 Cruisers x 10 Guns x 120 rounds x ( I am going to stick with 200 lbs) / 2000 lbs per ton / 2 islands -
240 Tons of explosive PER ISLAND
That's less than I had initially stated, but is still about a quarter of a Kiloton of high explosive per island, and the islands are flat, and the combined total land area is about 1500 acres. This means, with 4800 shells hitting the islands, you will have :
4800 shells / 1500 acres = 3 shells per acres.
And this is JUST the four heavy cruisers. It must be remembered: Yamamoto was on board the Yamato.
He was accompanied by the Nagato and Mutsu, arguablly the three most powerful battleships in the Pacific
at that time. And, the Ise, Hyuga, Fuso, and Yamashiro were accompanying the invasion force. Their guns
would have been available for the suppression of the defenses.
Yamamoto was going to be at the invasion PERSONALLY. This operation was HIS BABY ! For the IJN officers,
FAILURE WAS NOT AN OPTION ! If they had to use all seven battleships and the four cruisers to turn the
Midway Atoll into a sandy parking lot with Naval Gunfire, they would have fired their guns until the paint
blistered off the barrels !
Now, typically about 10% of shells on a battleship are HE, the rest being AP. And IJN battleships typically
carried about 100 shells per gun. Which means that they had 10 HE shells per gun. So:
Yamato: 9 guns x 10 shells x 3200 lbs / 2000 = 144 tons
Nagato/Mutsu: 2 ships x 8 guns x 10 shells x 2000 lbs / 2000 = 160 tons
Fusos/Ises: 4 ships x 12 guns x 10 shells x 1378 lbs / 2000 = 330 tons
For a Total of 634 tons of high explosive shells, or 317 tons per island. Add the 240 tons from the
cruisers, and you have more than 550 tons per island. Thats like each island being bombed by
about 275 B-17 flying fortresses, each with a maximum bomb load. And, the bombardment would
last for hours.
Paul R. Ward
One final note: If you go back to my original gunfire equation, and put in the figure of 253 lbs per HE Shell,
you get 303 tons of shells per island. My original back of the envelope calculatoin was 360 tons per
island. My bad.