Pushing hard science into history

I am amazed at how easily hard science intrudes into almost any subject. A few years ago I edited a volume of New Zealand naval memories for Random House – stories from participants in our Second World War sea battles. One of the accounts proudly explained that our light cruiser Achilles had been good for 36 knots, and pushed towards that at the Battle of the River Plate on 13 December 1939.

HMS Achilles of the New Zealand Naval Division at the Battle of River Plate, 13 December 1939. Artwork by John Lloyd. Lloyd, Arthur John, b 1884. Lloyd, Arthur John, b. 1884 :New Zealand's flag flies in the first naval battle of the war; H M S Achilles by skilful handling evades the shells of the Admiral Graf Spee [Auckland; 1940]. Ref: C-055-004. Alexander Turnbull Library, Wellington, New Zealand. http://natlib.govt.nz/records/23233527
HMS Achilles of the New Zealand Naval Division at the Battle of River Plate, 13 December 1939, flying the biggest New Zealand flag her crew could find (‘Make way for the Digger flag’, a sailor cried as he rushed deck-wards with it). Credit: Lloyd, Arthur John, b. 1884 :New Zealand’s flag flies in the first naval battle of the war; H M S Achilles by skilful handling evades the shells of the Admiral Graf Spee [Auckland; 1940]. Ref: C-055-004. Alexander Turnbull Library, Wellington, New Zealand. http://natlib.govt.nz/records/23233527
From a science perspective that didn’t add up, literally, because Achilles was designed for 32.5 knots. I knew that the draconian physics of ship propulsion made it impossible for Achilles to achieve 36. But the claim was emotionally genuine, and that made me wonder, so I set to work to figure out how Achilles actually performed at the River Plate – and why her crew had that belief in her speed.

That battle pitted Achilles, her sister ship Ajax, and the heavy cruiser Exeter against the German ‘pocket battleship’ Admiral Graf Spee. In theory the Graf Spee had it all over the British. Actually, the Germans were sent packing; and one of the ways the two light cruisers avoided much damage was by ramping up to maximum speed, well above Graf Spee’s modest 26 knots.

The eyewitness, in short, was right about the need for speed, even if his numbers were out.

But I wanted the numbers. I knew the speed Commodore Henry Harwood ordered the cruisers to make: 31 knots, essentially max tactical speed, with bit in hand for station-keeping. But was it feasible? First off in my analysis was design data. Achilles, a Leander class cruiser, was designed for 32.5 knots at 72,000 horsepower. However, the physics of marine propulsion are dismal. Ship hulls are typically optimised for cruising speed, and as a rule of thumb, power demand goes up by the cube of the speed. For Achilles, cruising at 16 knots demanded just 1/8 of the power needed to reach 32. I calculated that she would have had to generate roughly 115,500 horsepower to make 36 knots – quite impossible for her steam plant, even if it was pushed until it exploded.

HMS Achilles early in the battle, seen from HMS Ajax. Public domain, via Wikipedia.
HMS Achilles during the battle, seen from HMS Ajax. Note Achilles’ high wake – indicative of massive power output in shallow water. Public domain, via Wikipedia.

That wasn’t all, either. For Achilles to reach even her theoretical top speed of 32.5 knots demanded ideal conditions – not what was found off the Plate. Parameters that make practical maximum speed differ from design speed include actual displacement at the moment (variable, depending on consumables aboard), cleanliness of the hull, state of the propulsion plant, and especially depth of water.

Conveniently, Achilles‘ maintenance record is held by Archives New Zealand and the other data was also to hand. So! When battle opened Achilles was four months out of dock, well within the life of her anti-fouling paint. Barnacles and weed were not an issue. But she had just refuelled; and with full fuel tanks and munitions her displacement was close on maximum war load, affecting the water-plane area and cutting top speed below her peacetime design maximum. She was also two months overdue for a ‘two year’ refit, major maintenance intended to include ‘wear and waste’ tests on her boilers. She had been worked hard since the outbreak of war despite the delay. When the refit was eventually completed in June 1940, some 781 superheater tubes had to be renewed.

Achilles' aft turrets after the battle, with blistered paint from the heat of firing. I've put my hand on Y-turret, foreground - it's preserved at the Devonport naval base. Public domain,  New Zealand Electronic Text Centre http://nzetc.victoria.ac.nz/tm/scholarly/WH2-1Epi-fig-WH2-1Epi-b013a.html
Achilles’ aft turrets after the battle, with blistered paint from the heat of firing. I’ve put my hand on Y-turret, foreground – it’s preserved at the Devonport naval base. Public domain, New Zealand Electronic Text Centre http://nzetc.victoria.ac.nz/tm/scholarly/WH2-1Epi-fig-WH2-1Epi-b013a.html

All this hampered the ability of the ship to reach her design speed – but the main complication was that the battle was fought in shallow water. The thing about water is that (a) it has high mass for volume, demanding a lot of energy to move it; and (b) it’s incompressible in any practical sense, meaning that it acts as a solid object as far as energy transmission is concerned. What this means is that a ship in shallow water expends stupid amounts of propulsion power pushing a train of water from the sea floor to the surface – creating a huge wake – instead of pushing itself forwards. The wake phenomenon was observed by the crew at the time, and is visible in photographs. According to one account, when closer to the Plate, Achilles was unable to achieve more than 24-25 knots for this reason.

What happened during the battle was all the more extraordinary as a result. Achilles entered battle at around 14 knots, reaching 28 knots around 6.40 a.m. and working up to 31 knots by about 6.50 a.m. To do this under shallow-water hydrodynamic conditions meant radically over-stressing a tired steam plant – and in fact Achilles’ engineers managed to achieve 82,000 hp and 283 revolutions, well above design limits. What this added up to was that, irrespective of the speed actually reached, the ship was pushed absolutely flat out, a superlative achievement on the part of her engine-room crews. They kept it up through the battle in spite of fact that flames roared out of the furnace grilles and across the boiler room spaces with the shock of every salvo. Think about it. The word you want is ‘heroism’.

And that, my friends, explains the pride with which the performance was then remembered.

I put my reconstruction of what had happened into the book – Torpedo (Random House, 2007), with the science…and nobody noticed. Sigh. But you can read my other account of the battle, right now, in my book Blue Water Kiwis.

Copyright © Matthew Wright 2015

Sources: Archives New Zealand, Navy Department, 6/27/1, ‘HMS Achilles (Ship): defects, repairs and refits 1938-42’; R. J. McDougall, ‘New Zealand Naval Vessels’, GP Books, Wellington 1989; S. D. Waters, ‘The Royal New Zealand Navy’, War History Branch, Department of Internal Affairs, Wellington, 1956; Matthew Wright, ‘Blue Water Kiwis’, Reed NZ Ltd, Auckland 2001.

8 thoughts on “Pushing hard science into history

  1. Fascinating hydrodynamics and marine plant engineering here, Matthew. I especially like the bit about conditions in the engine rooms of Achilles at the height of the battle — very evocative. One of the things a lot of history does is to strive for the “big picture” from the general’s point of view rather than show what it was like for the privates. Yet if it wasn’t for what you quite rightly deem the heroism of the engine room crews, and all the other ratings and junior officers who stood to their posts and did their duty regardless of the conditions of battle, how would that big picture even be possible?

    Well done.

    1. Thank you! There’s no question that history – military especially – often looks just at the ‘top down’ side. There was a surge against that from the 1960s, looking instead to write ‘peoples histories’. I recall the first editor of the New Zealand Dictionary of Biography telling me in 1983 that he intended to subvert the old ‘top down’ pattern. Actually, I think both are necessary to get the broader picture. My professional historical work’s been labelled ‘post-revisionist’ locally in New Zealand because I’ve quite deliberately questioned what has become the orthodoxy. The usual reaction from strangers in the academy here has been a cascade of malice, but we won’t go there…

      All this said, NZ’s official WW2 histories (50 volumes penned 1949-65) always were written as a balance between that ‘top down’ and ‘bottom up’ story – by deliberate design on the part of the first editor, Maj-Gen Howard ‘Kip’ Kippenberger, who wasn’t just a soldier; he was a lawyer and a very capable scholar. They’re online if you want to sample any: http://nzetc.victoria.ac.nz/tm/scholarly/tei-corpus-WH2.html – I recommend Dan Davin and Jim Henderson’s ones, they were both professional writers as well as soldiers.

  2. Great post, Matthew! I did not know wake phenomenon. Your description of it made it very clear and easy to understand. I love detailed descriptions of naval battles. Too often, all you get is this ship and that one were sunk and the battle was one. Well, there’s much more to it than that. The details honor the courage of the men who fought the battles.

    The battle of the River Plate is just one example of why I scoff at the German navy of ww2. It seems to me they spent most of their time running away from a first-rate navy like the RN. There were no great clashes of naval fleets, just small actions. Had there been, I might speak admirably of Germany’s efforts. Unfortunately, their ships were used incorrectly as mere merchant raiders, a task suitable for a common destroyer. Most of the time, Germany’s finest vessels were hunted down in singletons like rats. Germany simply didn’t have a naval tradition and it showed in ww2.

    1. The hydrodynamics of it are fascinating, aren’t they. I was lucky enough with this battle to find a wad of personal accounts in the RNZN Museum – someone had tracked down every surviving sailor and got their story. It really brought the battle alive for me – and more. Achilles had spent the early part of the war in Chilean waters, and our guys were playing classic tourists. They finally took passage through Tierra del Fuego, en route to the South Atlantic, and the accounts of that journey were utterly extraordinary; here were these Kiwi blokes, half a world from their home, amidst a wild and icy landscape that none could have imagined ever existed.

      I agree about the German navy in WWII – they were mishandled. I think a part of that came from Hitler’s unease over deploying them, and part of the reason for the penny packet deployment, as I understand it, was that Adm. Raeder took every opportunity allowed by his mercurial leader, even if it meant sending out individual vessels. To this has to be added the failure of their designs – they’d lost their experienced design staff in 1919, and the result was that their WW2 ships were basically warmed-over WW1 designs. The ‘pocket battleships’ were a particularly faulty concept – basically they were over-gunned and very slow heavy cruisers, and Harwood’s force had it all over the Graf Spee in practise.

      1. Well, shucks. I may just have to buy you book, Blue Water Kiwis. The detailed account in there, yes?

        I was never impressed by the pocket battleship idea. It was undergunned against a true battleship, and not fleet of foot enough to to match cruisers.

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