In 1949 Sheaffer did another one of their surprise lane changes. They replaced the entire Triumph line with the Touchdown. While the Triumph line was named for the first pen model - sort of like US Navy ship classes - the Touchdown line is named for the filling system.
The Touchdown filler is pneumatic and includes a sac. It's not an intricate or complex filler but it is somewhat difficult to explain the technical details. I find it simplest to liken it to a bicycle pump. That's not entirely accurate, but it's not too far off the mark. Unscrew the knob, extend the Touchdown tube, submerge the nib/feed/section in ink, close the Touchdown tube, wait a few seconds for the sac to fill with ink. Wipe off the section and you are good to go. The operation, apart from the few seconds waiting at the end, is exactly the same as the Vacuum-Fil.
The primary failure mode of the Touchdown pens is the end of the barrel. There is an o-ring groove inside to provide a seal with the Touchdown tube. This is a very thin portion of the barrel and prone to cracking due to plastic shrinkage from UV exposure. This pen has been well cared for and exhibits no hint of shrinkage or cracking - see the photos. As long as it is not stored in a sunny spot it will last for many more decades.
Note this is a first year Touchdown pen. It is a larger diameter than the Touchdown Thin Model introduced in 1950.
The cap should bear a white dot. This is likely a replacement cap from a 1948 Sovereign. It fits perfectly and you'd not know it was incorrect unless you were a collector or went scouring the fabulous pages of @penherostore's web site. If you did, then you'd also see the nib has lost it's palladium plating. That doesn't hinder performance in the slightest.
The ink view grip section has ambered and it has a few scuff marks where some fool used pliers to open the pen. The section retains sufficient transparency to see the ink level. The scuffs have no sharp edges and become unimportant as soon as the nib touches the page.
The fine/extra-fine nib has been adjusted to write a wet, smooth line. The Touchdown filler is guaranteed for at least one year provided Noodler's ink is strictly avoided. That stuff stains plastics and melts rubber filler components.
Length Capped - 134 mm (5.26”) Uncapped - 114 mm (4.48”) Posted - 149 mm (5.8”). Diameter Cap - 12.7 mm (0.5”) Barrel - 11.5 mm (0.45”)