Found a new toy in John Warry's Warfare in the Ancient World, by Salamander Press.
   Essentially, its an interesting form of the Atlatl, that was used in battle. A javelin had a small hole drilled through the shaft. A cord was tied in the hole, and then wrapped around the javelin. A small loop was at the end of the cord.
  The thrower would wrap the loop around a fingertip, then do an overhead throw.  As he did this, the cord would unwind, starting the javelin spinning, like a bullet out of a rifle. The thrower then had to let go of the loop, and allow the javelin to go on its way.
    As with the sling, timing was everything.

This is not depicted with fletching. Apparently it's not needed, because of the spinning action

That's just arrow throwing, a sport described in Payne-Gallwey's The Crossbow.  It's also how the Saxons would put more power behind a spear thrown by hand.
  Tech, can you explain a little how fletching might add speed?  I would have thought that the drag effect would slow it down.