"Plunging Fire, Galena, and City Class Ironclads" Topic

I'm painting a City class ironclad. From the pictures I've got in Osprey and Gibbons, the top deck is made of wood, with armored pilothouse and wheel.

I seem to remember that the reason that Galena was a failure was because her decks were not armored, and that made her vulnerable to plunging fire. So the question is:

If this was really a critical issue, why wasn't this considered a defect in City class ironclads, as well?

It was a critical issue and it was a defect. Check the service records of the city-class; they had several serious hits from plunging fire, and one sunk (and raised later, iirc) by it, I think.

Vulnerability to plunging fire was an issue, but was hardly the only hazard faced by the ironclad gunboats. Using the City class as an example, five were sunk due to enemy action during the war. Cairo and Baron de Kalb (formerly St. Louis) were lost to mines. Cincinnati and Mound City were sunk by ramming but were both raised and put back into service. Cincinnati was sunk (and raised) again by plunging fire in the incident related above by doc mcb. There were a number of disabling hits taken by City class gunboas during actions against Confederate forts, but the overall usefulness and performance of these vessels (the USS Carondelet had the most battle honors of any US Navy vessel prior to WW2) seems to have ensured their continued use. The Navy was aware of the problem and seemed to have just lived with it, since they didn't engage prepared forts on high ground every day.

Galena wasn't a failure because it's decks were unarmored, Galena was a failure because it's armor was too weak. The entire armored side was caved in at Drewry's Bluff.
-Kle.

The Galena was holed in the side so many times it might as well not have been armored. The combnination of weak armor plating and the high angled fire from guns on the bluff rendered the armor ineffective.

As for the City class…quantity has a quality all of its own. The vessels had flaws – see the list above – which the Navy worked to correct throughout the war with varying degrees of success.

Great answers – thanks to all!

In general every civil war era ironclad was weak against plunging fire. At most, the biggest monitors only had 2" of deck armor. Most ships had no deck armor at all. In fact many monitors and ironclads had simple grates rather than decks over the turret and casement to relieve the crew from smoke and heat, a more pressing every day problem. However, this lack of deck armor became an issue for the city class ironclads as they were among the few ships that actually took plunging fire (most notably while attacking the bluffs at Vicksburg). In general, plunging fire was not used against ships during the war. Most engagements consisted of level firing at short range with the hope of jarring the enemy armor loose thru brute force. Therefore each side put as much armor in this direction as their manufacturing ability allowed. Generally, thee rebels would provide up to 6 inches of side armor in layered 2" plate. The Union had better manufacturing ability and was capable of up to 12" on the late war monitor turrets.

If you are looking for weakness in the city class design you have the following. 1) fire tube boilers that were prone to dangerous explosions or steam releases if damaged. A common problem in the western waters that led to the Sultana disaster. 2) guns far smaller than similar purpose ships made in the coastal yards. 3) inefficient design compared to the monitors. It required a larger area of iron to cover the casement, therefore limiting the maximum armor thickness at any one point. 4) lack of underwater armor or mine sweeping equipment. Torpedoes and rams were a greater threat than enemy gun fire. 5) unseasoned wood (rot problem in southern swamps)

It is a tribute to the CAIRO class ships and to their crews that they achieved as much as they did -- they were key instruments to the US victory in the west. They took a LOT of damage from Confederate fire, not to mention from ramming and torpedoes. I don't know what the total loss of life among their crews was, but it was not light.

The Galena had sloping sides, or curved from the waterline. In theory a shot fired at the side of the ship from another level with the water would hit a sloping armored side and either be stopped, or bounce off at an angle.

Plunging fire against the sloping side was falling shot which actually would hit the armor dead on, or at an angle while did not allow much in the way of "bounce".

Thus, instead of getting the advantage of angled armor, the ship was subjected to flat trajectory fire in effect.

Dan

IIRC Mound City took a hit from a Confederate rifled field piece that pierced the armour and ruptured the boiler drum. The subsequent explosion and release of high pressure steam killed almost everyone on board. The City class were meant to be lightly armoured shallow draught gunboats, not ocean going iron clads. I believe the paddle wheels were unarmoured. The grates above were needed to provide ventilation and combustion air for the boilers.
The C.S.S. Arkansas had boiler plate on the deck to make it "look" armoured.

As Dan Cyre said the effewct of plunging fire was not that it went through the grate on top, it was that it hit the armor at a flat angle. I can't say as I've ever heard of a ship taking a round in the grateing.

The problem with the Galena was the design of the armor. It was laid in strips, backed with rubber. Sort of like taking railroad rails and interlocking them to make armor. Didn't work at all. The rouns would hit and spread the strips and go in. All the armor was stripped after Fort Drewry and she served as a screw frigate the rest of the war.