Since 1841, Leech had been producing sketches for wood-cut engravers for print and had been from all accounts prolific. Renown as a humorist, Leech was by the time of the war also producing for London Illustrated and had by this time achieved what was his zenith as an illustrator.
Leech was subtle in his handling of subject matter and not as brutally critical as some of his contemporaries. As you can see they are well observed and generally fall within the artistic sketching or illustrative end of the cartoonist's spectrum. Leech was famed for more than his work for Punch and it may not be truly accurate to even discribe him as a cartoonist at all.
Aged 36 at the time war broke out, John Leech was only to live a further 11 years, dieing on 29 October 1864 aged 47. Whilst this posting contains what I believe to be the most pertinent Crimean observations by Leech, a more complete archive can be found at http://www.john-leech-archive.org.uk/