E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Jack the Giant-killer
owed much of his success to his four marvellous possessionsan invisible coat, a cap of wisdom, shoes of swiftness, and a resistless sword. When he put on his coat no eye could see him; when he had his shoes on no one could overtake him; his sword would cut through everything; and when his cap was on he knew everything he required to know. Yonge says the story is based on the Scandinavian tale of Thor and Loki, while Masson maintains it to be a nursery version of the feats of Corineus in Geoffrey of Monmouths marvellous history. I apprehend that neither of these suggestions will find many supporters.
Military success depends (1) on an invisible coat, or secrecy, not letting the foe know your plans; (2) a cap of wisdom, or wise counsel; (3) shoes of swiftness, or attacking the foe before he is prepared; and (4) a resistless sword, or dauntless courage.