August 21, 2008

Flight Deck Round-Downs... Why?

The early days of aircraft carrier design saw a lot of different concepts that eventually went by the wayside.  Such "innovations" as multiple flight decks (so airplanes could launch directly from their hangars),  transverse-mounted catapults that launched planes perpendicular to the direction of travel (ditto), longitudinal arrestor wires, arrestor gear at both bow and stern (so if one end of the flight deck had a hole in it, the ship could steam in the other direction and launch planes from the undamaged end), carriers without islands, the list goes on and on.  All of these elements made sense, however, and one can see why an Admiralty could think they were good ideas at the time.

One design feature of some early carriers, however, has always struck me as being particularly pointless, with no redeeming features whatsoever: the flight deck round-down.

HMS Hermes
As can be seen in the above picture, a round-down is a sharply sloping portion of the aft end of a flight deck, a location particularly unsuitable to topography of any sort.

IJN Akagi, circa 1927-'35.  Note the "fly-off" decks, right, round-down left.
In the book Shattered Sword, it's mentioned that the Akagi's round-down is so pronounced that it, in effect, shortens her flight deck, as planes cannot be spotted there without having them roll off into the sea.

So why are they there at all?  Throughout all my readings through the years, the only reason I've seen is that they were thought to be aerodynamically helpful for landing planes, perhaps by creating an are of calm air behind the ship.

But even if that were so, doesn't it seem that it'd be a rather ill-positioned lee for an aircraft attempting to land, not to mention small?  Further, they also look like a fairly hostile place to try and land upon in the first place.  Imagine: you touch down on the round-down, crest the "hill", and then?  You're thrown back into the air, much like today's "ski-ramp" carrier decks would do.

Do any of you, my readers, have an idea?  I'm completely flummoxed here!

Posted by: Wonderduck at 11:12 PM | Comments (4) | Add Comment
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I wonder if they thought of it as a way to make the initial contact just a bit more forgiving. If you came in just a bit too low, then if the flight deck was level you'd run into it, but with that dip you might bounce off and still have a chance of catching the arrestor cable.

I don't think it would work, but I wonder if that's what they were thinking?

Posted by: Steven Den Beste at August 21, 2008 11:22 PM (+rSRq)


The variation in forms of early aircraft carriers mirrors the variation in forms of early combat aircraft two decades before. The thing is that we see the mature aircaft, and the mature carrier, and know what they look like, but the people back then didn't.

Obviously, what we're seeing is the result of their experimentation and evaluation, to determine what works and what doesn't. For instance, it always gets me just a little to see WWII carriers without angled flight decks. It just seems to obvious that a carrier should have such a thing, yet it wasn't until the end of WWII before anyone (the Brits) even thought of such a thing.

Posted by: Steven Den Beste at August 22, 2008 11:24 AM (+rSRq)


I remember reading a book about Ark Royal iii (the WW2 one), which said the flight deck's was deigned to give better air flow, therefore helping take off. (British naval aircrst in the inter war years being... antiquated to say the least). Not sure about landing though,

The later Illustrious class had a similar shaped flight deck, later more powerful  aircraft didn't need the assistance and at least one (Indomitable?) had the bow and stern rebuilt post war.

Posted by: Andy Janes at August 22, 2008 03:32 PM (xVeNB)

4 I believe it was to accommodate the original longitudinal arrestor wires. Once the now standard transverse arrestor wires were implemented, the rounding was no longer needed. They didn't build carriers with it any more, but they didn't spend the money to flatten it out either. 

Posted by: Paul Fitch at February 05, 2013 01:09 PM (M/vyn)

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