Now, in getting under weigh, the station generally occupied by the pilot is the forward part of the ship.
Now, in getting underway, the station generally occupied by the pilot is the forward part of the ship.
The astute reader will recognize the problem sentence from Herman Melville’s Moby Dick (which I refuse to hyphenate). I was quite astounded when I first read it—and astounded anew when I saw the spelling “under weigh” again later on in the book. There is no difference in usage from our own “underway”: it’s just spelled as two words, and “weigh” is used instead of “way”.
Curious to see when the change occurred, I checked my favorite free online English etymology website (Etymonline.com), and was quite astonied to see that the entry for “underway” makes absolutely no mention of “under weigh”! Perhaps, I thought, this was simply an idiosyncratic feature of Melville’s writing, and everyone else used “underway” before and after. But lo! Etymonline.com lists the date of origin as 1934 (with reference particularly to ships). Moby Dick was published in 1851.
Without a paid subscription to the OED, I don’t think I can solve this puzzle. I will note, though, that the spelling “under weigh” appears in even older works (I heard rumblings about it appearing in The Count of Monte Cristo), and also that there’s no question that “underway” is the correct spelling at this point in time. However, it also seems to be the case that “under weigh” is older than “underway”, and that the two expressions mean roughly the same thing. I’ll leave it to you to draw your own conclusions.
Oh, and here’s a freebie: The title is properly “anchors aweigh”, not “anchors away”. It would seem that the US Navy has successfully preserved that expression, at least.