Interesting question from Steve.........

Source: Did the British ever deliver gas in artillery shells?

Yes - however I am surprised at the extent of it;s usage.

A quick look at Farndales History of the Royal Regiment of Artillery Western Front 1914 - 1918 shows a number of references for Shells, Gas.

The first mention is in the planning of the Somme bombardment. Indeed the official history out lines "shelling of communications every night (but lacrymatory shell was not to be used until midnight on Y/Z day)". Information on this type of shell can be found on this post Lacrymatory Shell - What is it ?.

The next mention is The Battle of Thiepvaal Ridge in September 1916 where it is outlined that the firing of gas shells by 4 inch mortars was a new tactic in the war.

In the Battle of Messines 1917, part of the ammunition preparation included 120,000 rounds of gas shell. for the 18 pounders. During the battle, gas shelling by 4.5" howitzers supported the IV Corps front. The plans by General Uniacke (MGRA Fifth Army) for the initial phase of 3rd Yrpes specified "Enemy batteries which could provide defensive fire were to be bombarded with gas from Zero Day minus One to Zero Day.

At Cambrai, the operational order stated that, at H hour , all 60 pounders were to open on the German guns with gas shell, then switch to known reserve areas.

Preparations for the Battle of Amiens, August 1918, saw 50,000 rounds of 6 inch gas shell being dumped. Counter Battery fire was given top priority by the Gunners, and gas was used freely. In the plan for the attack on the Hindenberg Line, September 1918, the guns of the Fourth Army would from 2200 hours 26th September to 0600 hours 27th September fire a barrage of mustard gas onto all known trenches and gun positions along the whole front. 32,000 rounds of the new BB gas shell were fired.

Ammunition

This post shows "Mother" the 9.2 inch howitzer at the Imperial War Museum with a chemical shell on it's loading tray. I am assuming chemical = gas ?

Mother" at IWM what's the blue-Grey projectile ready for loading ?

Shell BL Chemical 9.2"

The 18 pounder chemical shell is the Grey one third along

RA Museum - Firepower 18 pounder ammunition