 In their first year , Led Zeppelin completed four US and four UK concert tours , and also released their second album , Led Zeppelin II . Recorded mostly on the road at various North American studios , it was an even greater commercial success than their first album , and reached the number one chart position in the US and the UK . The album further developed the mostly blues @-@ rock musical style established on their debut release , creating a sound that was " heavy and hard , brutal and direct " , and which would be highly influential and frequently imitated . Steve Waksman has suggested that Led Zeppelin II was " the musical starting point for heavy metal " . 
