C. Bates Lieutenant
Air Force (Retired) (
Sea, Swell and Surf Forecasting
for D-Day and Beyond
The Anglo-American Effort, 1943-1945
FULL 38 page long PDF. http://scilib.ucsd.edu/sio/hist/bates_sea-swell-surf.pdf
Extracts from page 1 to 18 – Invasion
(planning stage): …….Admiral Ramsay knew it would be impossible to control
an invasion fleet of 1,213 naval combatants, 4,126 landing craft/ships,
736 naval auxiliaries, and 864 merchant vessels.
Eisenhower made the tense situation worse during Friday, June 2.
With the proposed D-Day just three days
away, "Ike" advised Stagg that he now required weather
briefings during both morning and evening hours. ……..
…… the majority's prognosis that the proposed D-Day of June
5would feature rain, high seas, and low clouds within the assault
area. Then, after listening to this updated forecast, as of 0430
DBST Eisenhower ordered this massive invasion involving 500,000
personnel postponed for 24 hours. …..
at noontime stations on Ireland's west coast reported a major cold
front moving eastwards at 30 knots that was certain to pass through
the Normandy assault area during early Monday, June 5. …….
Page 18 to 20
Wave Forecasting for the "Big Storm" (19-22 June 1944)
The section is reprinted in full
June 6th, Section
activities were quiescent for the next 11 days with one exception.
During D-plus-8 (14 June 1944), Lt. Crowell reported for duty
complaining of shrapnel rattling around his wash basin in Half Moon
Street because of low-flying German
aircraft during the night. These aircraft, of course, were the pesky
"doodle bugs" with 850 kilogram (1,870 pound) warheads
that soon would be impacting Greater London an average 80 times per
day. Even so, denizens of the Citadel had nothing to fear for their
windowless structure was capped with 20 feet of concrete. Unknown to
us, however, was the War Office's ongoing use of 600,000 tons of the
same material for building artificial harbors off the OMAHA and GOLD
beachheads by D-plus-21 (27 June 1944).
a "MULBERRY," such a harbor would be approximately the
and enclose a square mile of beach front featuring a 21 foot change
in sea level during spring tides. On the deep water side, three
lines of barriers would suppress incoming waves. Furthest out were a
row of Admiralty-designed BOMBARDONS comprised of 24 free-floating
but anchored steel cruciforms with a 19 foot draft. At mid point
and firmly emplaced in a low tide water depth of 30 feet were 26
PHOENIXs consisting of massive free flooding concrete caissons each
200 feet in length. Then close in for the protection of small craft
were "CORNCOBS," a string of antiquated ships
intentionally scuttled into 10 feet of water at low tide. Finally,
for rapid ship-to-shore transfers several miles of floating roadways
extended out to Lobnitz pierheads that moved upwards or downwards
with the tide level. As for a MULBERRY's ability to withstand wave
action, its prime designer, Brigadier Bruce White, CBE, RE, assumed
it would stay intact throughout a conventional summer storm
featuring Beaufort Force 6 winds (approximately 24 knots) (White,
told, 35 convoys moving as slowly as 3 knots were required to bring
the MULBERRY paraphernalia across the Channel. Scheduling such
convoys fell within the purview of Admiral Ramsay. Accordingly,
Commander Fleming noted later:
was decided that the most important convoy of all carrying very
large quantities of essential heavy equipment should, if possible,
be held back until there were prospects of a period of 48 hours with
little or no wind and calm seas. By 17th June (D plus 11),
it appeared that ideal conditions would prevail for the next two
or three days .... On the strength of my forecast to this effect,
the [100 tug] convoy was ordered to sail on 18th June.
Unfortunately, at this very time, both Fleming and Stagg's
SHAEF team of meteorologists fell into a "sucker's hole."
Based on prior episodes, they predicted a lobe of 1,030 millibars
pressure would extend northeastwards from the Azores into the
area, thereby allowing calm seas. Instead this lobe's center paused
while a low pressure zone moved up from southern
. Consequently, from June 19th through June 22 near gale
force winds blew from the northwest directly down the Channel for
120 miles. Thus, Ramsay's special convoy became a total wreck.
Fleming further remembers:
“If previously I had never experienced sheer misery, I
certainly did now, and the fact that I was living in close contact
with those responsible for ordering the operation was as salt in my
wounds ... the feel that one had been, however inadvertently, the
main contributor to what was almost a major disaster is something
not easily put aside."
the onset of the storm was not predicted, pandemonium reigned
throughout the beachheads. Fortunately, northwesterly winds offered
only a glancing blow to the British sector so its MULBERRY-B, now
called Port Winston, and associated small craft suffered only
moderate damage. Off
, however, aboard the
flagship USS AUGUSTA, Commander Steere was reporting maximum wave
heights of 12 feet and wind gusts up to 32 knots. Inshore, chaos.
With inadequate holding tackle, 800 landing craft collided with each
other or stranded on the beach. Early on, five break away LCTs hit
the floating roadways and caused them to buckle badly, thereby
dooming the pierheads from future use. Even worse, the 200-foot long
BOMBARDONs broke loose and struck the embedded PHOENIXs, damaging 21
out of 31 of those vital blockships beyond repair.
the time, it did not seem possible but all storms must end. In
anticipation, during the mid-afternoon of June 21st (D-plus-lS),
's convoy dispatcher called Admiralty for advice as to when
beachhead surf heights would drop to a tolerable level, i.e., to
four feet or lower. As the wave specialist on duty, the author
indicated 24 hours hence. In the storm's aftermath, after inspecting
the American's MULBERRY-A, Rear Admiral Kirk recommended its
abandonment. During 2 July 1944 (D-plus 26), General Eisenhower
concurred even though
was still nearly useless and Breton's ports of
, St. Nazaire, and
were far from being captured. In other words, the requisite 20,000
tons of daily supplies for what was now the 1st and 3rd
U.S. Armies must continue primarily arriving over the beachheads.
38 page long PDF. http://scilib.ucsd.edu/sio/hist/bates_sea-swell-surf.pdf