Upvote:4
From what I've found, the Ju 88 was updated during the Battle of Britain:
A series of field modifications were made to make the Ju 88 less vulnerable, including the replacement of the single MG 15 rear machine gun by a twin-barreled MG 81Z machine gun and the fitting of additional c**kpit armour.
Other than field modification, a newer version (A-4) was produced:
The flagship Ju 88 A-4 went into service during the closing days of the Battle of Britain. Although slower than the A-1, it solved nearly all of the troubles of the A-1. The A-4 actually saw additional improvements including more powerful engines but, unlike other aircraft in the Luftwaffe, did not see a model code change. The Ju 88 C-series also benefited from the A-4 changes.
Here the full characteristic of the A-4 variant:
Improved variant. Longer wingspan, due to redesigned wingtips. Stronger defensive armament. Power provided by Jumo 211 J-1 or J-2 engines producing 1,050 kW (1,410 hp), driving wooden bladed propellers. Reinforced undercarriage. Provision for four external bomb racks.
Here a detailed view of the changes of the A-4 version:
The A-4 was the most important version of the Ju 88A. It solved the problems that had limited the performance of the A-1, most especially by increasing the wingspan of the aircraft by nearly six feet to 65ft 7.5in. It used more powerful 1,400hp Jumo 211F or 211J engines, which made up for a general increase in weight. Part of that increase came from an improvement in internal armour, especially around the c**kpit. The A-4 now carried five guns – one fixed forward firing in the windscreen and four flexible guns, one in the lower nose, one rear facing in the ventral gondola and two rear facing in the dorsal position. The MG 15 was normally replaced by the belt-fed MG 81, which had a higher rate of fire, or by the twin barrelled MG 81Z or 13mm MG 131s. The A-4 could carry up to 7,936lbs of bombs, with 2,200lb in the internal bomb bays and the rest on the four ETC bomb racks under the wings. Production of the A-4 was pushed back by delays to the Jumo 211F and K engines, but it had entered service in time to take part in the invasion of Russia in June 1941. The gap was filled by the interim A-5 version. The A-4 was the main service version by early 1942.
Note: the wikipedia page report sizing and armaments referred to the A-4 version.