>submerged obstacles
Is that the new name for 'low tide'?
Utmost Savagery: The Three Days of Tarawa by Col. Joseph H. Alexander, USMC (Ret.) In his book on page 76 and 77 he gives a good overview of the subject of low tide on the coral reef at Tarawa. He actually pulled from an essay written by Donald W. Olson, professor of physics at Southwest Texas State University. The Essay entitled “The Tide at Tarawa” was published in Sky and Telescope magazine, 1987.
" Olson explains that low tidal ranges are not only affected by quadrative factors, that is, the twice-monthly neap tides caused by the moon being in its first or last quarters, a relationship understood by mariners for thousands of years. Much less appreciated is the effect of the moon’s monthly orbit, which creates increased tidal ranges at it’s perigee-when it’s closest to earth-and decreased tidal ranges at its apogee-when it’s farthest from earth. The combination of a perigean and spring tide is often enough to cause coastal flooding. Conversely, when an apogean tide coincides with a neap tide, the range will be uncommonly low." (76)
…“He found only two dates in 1943 when apogee occurred within twenty-four hours of quadrature, 12 April and 19th November….As Dr. Olson concludes: “Thus the landing at Tarawa was scheduled for one of only two occasions in 1943 when apogean neap tides could occur….In fact, from 9am until 10pm on D-Day the water hovered within six inches of its mean level, 3.3 feet…”
Utmost Savagery: The Three Days of Tarawa by Col. Joseph H. Alexander, USMC (Ret.)
Pg. 76 and 77.
“The Tide at Tarawa”, Sky and Telescope Magazine, Nov. 1987, 528. Dr. Donald W. Olson.
https://www.usmilitariaforum.com/forums/index.php?/topic/359820-the-low-tide-on-the-reef-at-tarawa/