While Alfred's little army slowly began to gather at Athelney, the king himself set out to penetrate the camp of Guthrum, the commander of the Danish invaders.

【译文】阿尔弗雷德人数不多的军队开始在阿塞尔纳慢慢集结时，大帝亲自潜入丹麦侵略军司令官古瑟罗姆的营地。

【讲解】the king himself指Alfred the Great。Guthrum是入侵英国的丹麦军首领。公元878年5月，被阿尔弗雷德大帝战败，改奉基督教，并认阿尔弗雷德大帝为教父。

【单词和短语】

set out 出发
We set out with enough provisions.
我们带上足够的食品出发了。

penetrate：深入；进入；打入（to succeed in becoming accepted into a group or an organization, sometimes in order to find out their secrets），

例如：
penetrate the territory of enemies渗入敌人领土

penetrate an enemy organization打入敌人组织

Our troops have penetrated (into) enemy territory.
我部队已深入到敌占区。

penetrate的名词形式为penetration。

penetrating adj. 敏锐的，尖锐的，有穿透力的

His dark and penetrating eyes seemed to pierce the shelter of her veil.
他那双锐利的黑眼睛好象刺穿了她那块面纱的遮蔽。