The Sheaffer Snorkel pen is what I believe to be the pinnacle of fountain pen development. It is a wonderfully over-complicated piece of handwriting equipment.
The Snorkel was a logical development of the W. A. Sheaffer Pen Company's "TipDip" line of fountain pens. The TipDip pens had a ink-intake in the nib support so that you didn't have to plunge the whole of the nib, just the front half of the nib, in the ink in order to take up ink into the resevoir.
Unlike other fountain pens, the TipDip had a pneumatic system for compressing the ink bladder inside. In order to fill the pen, you would unscrew the back, allowing the metal inner sleeve to be pulled out from the plastic barrel of the pen. There was an O-ring which sealed the inner compartment. Then, the operator would insert the tip of the pen into ink and quickly push the inner sleeve back into the barrel of the pen. This would create a positive pressure within the pen, compressing the inner rubber bladder. At the bottom of the stroke, an indentated slot in the metal sleeve would allow air to escape the pen as the slot crossed the O-ring. The pressure being relieved, the ink sac would reinflate under it's own power, and ink would be drawn into the sac.
The Snorkel went one step more complicated from the TipDip line. During the process of unscrewing the back of the pen, a thin metal tube would protrude from the front of the pen. This would allow the pen's operator to fill the pen without having to dip the nib into the ink, thus saving the effort of having to wipe the ink from the outside of the nib.
There were at least two styles of Sheaffer pens that had this mechanism. The first was the thinner "Snorkel" model. The other was the much-more-expensive-due-to-collector-interest "PFM", or "Pen For Men", which was roughly twice as thick around the middle as the Snorkel...
Even though the mechanism is more complicated than a pen needs to be, they perform remarkably well, and can be refurbished rather simply, with a change of seals.