Photo from Karl Kjarsgaard, director of Bomber Command Museum of Canada.
He also sent Halifax Print of Halifax B. Mk. III LW170. 
Wikipedia has more about the background of "Bless 'Em All".
You may listen to Vera Lynn: Bless 'Em All or George Formby: Bless 'Em All.
The point is that it takes all kinds of people to get a Halifax ready for a mission.

Brian Walters kindly added this:
"The bomb trolley in front of the aircraft is carrying a typical mixed bomb load comprising of 1000 pound medium capacity bombs, 1400 pound general purpose bombs and a canister containing a large number of incendiary “bomblets” which
were discharged from the canister during its descent.

In addition to the usual ground crew, those men who worked tirelessly in all kinds
of weather out on the dispersal stands where the aircraft stood to reduce the chances of damage to an aircraft either from enemy action or accident on another aircraft close by, there were the armourers who loaded up the bombs, the armourers who specialised on the guns, the radio fitters who installed the specialist communications equipment such as the H2S bombing radar, made sure that the correct crystals were fitted to the VHF radios and that the correct frequencies were locked onto the T1154 HF radio transmitter.

The refuellers attended with their fuel bowsers or tankers to top up the fuel tanks with the quantities of petrol requested by the Flight Engineer and the ground crew engine mechanics made sure that each engine had been turned over by at least two revolutions by hand before start up to prevent the engine oil collecting in the lower cylinders causing what was called a “Hydraulic lock” and damaging an engine. This was a problem with the sleeve valve radial engine such as the Bristol Hercules.

Then there were those little jobs which few people even think about such as refilling the crew’s compressed oxygen bottles and bringing on board the homing pigeons and if necessary checking and replacing the dinghy and other survival equipment.

When the ground crew’s work was done and the seven members of the aircrew arrived at the dispersal, the senior NCO of the ground crew would almost begrudgingly lend “his” aircraft to the aircrew for the duration of the sortie and the pilot in his capacity as Captain would accept the aircraft after conducting his own pre-flight checks by signing the appropriate page in the RAF Form 700.

Before the aircrew even set off to their aircraft there were things which had to be done, on a personal note, there was the letter “To be delivered in the event of my death” and all the superstitions which must be carried out in the correct order to guarantee a successful op, there were the various briefings, target, meteorology, navigation points, weapons brief and so on. And then to the pre-flight meal, traditionally of bacon and eggs, then pick up their rations for the trip from their respective messes, a sandwich, some boiled sweets and chocolate and a thermos flask of hot soup which usually smelt like rubber for some reason then it was over to the flight safety section to collect their parachute packs which they carried to the aircraft and stowed in the appropriate carrier in the aircraft. The pilot’s parachute was often already installed in his seat, but the rest of the crew would have to clip their parachutes onto two large “dog lead” type clips on the chest part of their harnesses."

See also Emergency equipment and exits - Lancaster I.

After a question Brian added on 17 MAR 2018,

"Regarding the bomb release mechanisms, as far as I know the bomb aimer could select to drop bombs individually or all at the same time. He could also elect to drop the bombs in a timed "stick"; after he'd pressed the release button the release "computer" could then release the bomb load in a preset pattern and at preset timed intervals, often set to something like a half second between each bomb release. There were a number of bombs which looked like a canister, they were usually known as HC or High Capacity bombs but they were wider in construction and were usually 4000 or 8000 lb devices often called "cookies". Cookies were dropped as just a canister without aerodynamic flights on the tail end. The way that the incendiary canister works was a small parachute was deployed during the fall which operated a mechanism to open the sides of the device allowing the small incendiary bombs to fall out. The other large bomb which took the shape of a canister was the "Blockbuster".

One serious deficiency of the Halifax over the Lancaster wasn't so much the total bomb load which in the earlier versions of the Lancaster were fairly similar, but the physical size of the main bomb bay. The Lancaster was to all intents and purposes built as a bomb bay with wings which, if anybody who has tried to move around inside the 'Lanc' would have no doubt found whereas the Halifax while still somewhat cramped especially in full flying kit was easier, largely due to the smaller main bomb bay. The bomb load was increased by the use of the two wing bomb bays between the fuselage and the inboard engines. The Lancaster in its later variants with uprated engines and other modifications able to carry the 5 ton "Upkeep" mine, the 5 ton "Tallboy" and the 10 ton "Grand slam" aerodynamic bombs. This deficiency meant that although the Halifax entered service a few years before the Lancaster, the Halifax force fell out of favour with ACM Harris in favour of the Lancaster and secondly, the Halifax was unable to carry such large weapons as the 8000lb high capacity bomb, the "Cookie" without modification, even though a Halfax was the first aircraft to carry and drop the 8000 pounder in tests."