I am reading "Rockets, Missiles, and Men in Space" by Willy Ley,
and was amazed to read that the V2 used "film cooling" or "transpiration".
It had 4 rows of holes letting fuel into the throat of the nozzle to make
a cool film protecting the nozzle from the hot gasses. I knew they
used the fuel for regenerative cooling but did not know they also
used it for film cooling. A google search confirmed this with:

http://www.wsmr-history.org/InsidePhotos5.htm

This extra fuel also made the exhaust flame like 50 feet long instead
of maybe 10 feet long.

Ley's book is a nice history of rockets, though only up till the date of
the book, which could be in the 50s or 60s depending on which edition
you get (and the name changed a bit too).

-- Vince