Hello! Sorry for the delay in the answer. This is a basic bibliography mainly focussed in the military matters, although there are many other subjects involved in the game's research.
General history:
- Philip Abels, Richard: Alfred the Great - War, Culture and Kingship in Anglo-Saxon England. Routledge.
- Pollard, Justin: Alfred the Great. John Murray General Publishing Division.
- Ryan Lavelle, Ryan: Alfred's Wars: Sources and Interpretations of Anglo-Saxon Warfare in the Viking Age. Boydell Press.
- Holman, Katherine: Historical dictionary of the Vikings. Scarecrow Press.
- Roesdahl, Else: The Vikings. Penguin Books.
- Marren, Peter: Battles of the Dark Ages. Pen & Sword Military.
- Graham-Campbell, James: The Viking World. Frances Lincoln Publishers.
Weapons and warfare:
- Siddorn, Kim: Viking Weapons and Warfare. Tempus Publishing.
- Chartrand, R; Durham, K; Harrison, M; Heath, I: The Vikings - Voyagers of Discovery and Plunder. Osprey Publishing.
- Peirce, Ian: Swords of the Viking Age. The Boydell Press.
- Pollington, Stephen: English Warrior from earliest times to 1066. Anglo-Saxon Books.
- Halsall. Guy: Warfare and Society in the Barbarian West 450-900. Routledge.
War horses:
- Hyland, Ann: The Medieval Warhorse From Byzantium to the Crusades. Grange Books.
- Davis, R.H.C.: The Medieval Warhorse - Origin, Development and Redevelopment. Thames & Hudson.
Ships:
- Shetelig, H.; Brogger, A.W.: The Viking Ships - Their Ancestry and Evolution. Dreyers Forlag.
- Crumlin-Pedersen, Ole: Skuldelev Ships 1 (Ships and Boats of the North). Viking Ship Museum/National Museum of Denmark.
- Crumlin-Pedersen, Ole: Viking-Age Ships and Shipbuilding in Hedeby/Haithabu and Schleswig: 2 (Ships and Boats of the North). Viking Ship Museum/National Museum of Denmark.
- Thirslund, S.; Thirslund, Soren: Viking Navigation. Viking Ship Museum/National Museum of Denmark.
Clothing:
- Ewing, Thor: Viking Clothing. Tempus Publishing.
- Owen-Crocker, Gale R.: Dress in Anglo-Saxon England. Boydell Press.