 Hoover Dam opened for tours in 1937 after its completion , but following Japan 's attack on Pearl Harbor on December 7 , 1941 , it was closed to the public when the United States entered World War II , during which only authorized traffic , in convoys , was permitted . After the war , it reopened September 2 , 1945 , and by 1953 , annual attendance had risen to 448 @,@ 081 . The dam closed on November 25 , 1963 and March 31 , 1969 , days of mourning in remembrance of Presidents Kennedy and Eisenhower . In 1995 , a new visitors ' center was built , and the following year , visits exceeded one million for the first time . The dam closed again to the public on September 11 , 2001 ; modified tours were resumed in December and a new " Discovery Tour " was added the following year . Today , nearly a million people per year take the tours of the dam offered by the Bureau of Reclamation . Increased security concerns by the government have led to most of the interior structure being inaccessible to tourists . As a result , few of True 's decorations can now be seen by visitors . 
 Hoover Dam opened for tours in 1937 after its completion , but following Japan <a href='null_genetive' title='1'><mark>'s</mark></a>attack on Pearl Harbor on December 7 , 1941 , it was closed to the public when the United States entered World War II , during which only authorized traffic , in convoys , was permitted . After the war , it<a href='been_done' title='2'><mark></mark></a> reopened September 2 , 1945 , and by 1953 , annual attendance <a href='been_done' title='3'><mark>had</mark></a> risen to 448 @,@ 081 . The dam closed on November 25 , 1963 and March 31 , 1969 , days of mourning in remembrance of Presidents Kennedy and Eisenhower . In 1995 , a new visitors <a href='null_genetive' title='4'><mark>'</mark></a>center was built , and the following year , visits<a href='been_done' title='5'><mark></mark></a> exceeded one million for the first time . The dam closed again to the public on September 11 , 2001 ; modified tours <a href='uninflect' title='6'><mark>were</mark></a> resumed in December and a new " Discovery Tour " was added the following year . Today , nearly a million people per year take the tours of the dam offered by the Bureau of Reclamation . Increased security concerns by the government <a href='been_done' title='7'><mark>have</mark></a> led to most of the interior structure being inaccessible to tourists . As a result , few of True <a href='null_genetive' title='8'><mark>'s</mark></a>decorations can now be seen by visitors . 
Hoover Dam opened for tours in 1937 after its completion , but following Japan  attack on Pearl Harbor on December 7 , 1941 , it was closed to the public when da United States entered World War II , during which only authorized traffic , in convoys , was permitted . After the war , it been reopened September 2 , 1945 , and by 1953 , annual attendance done risen to 448 @,@ 081 . The dam closed on November 25 , 1963 and March 31 , 1969 , days of mourning in remembrance of Presidents Kennedy and Eisenhower . In 1995 , a new visitors  center was built , and the following year , visits done exceeded one million fa tdafirst time . The dam closed again to thdaublic on September 11 , 2001 ; modified tours was resumed in December and a new " Discovery Tour " was added thedallowing year . todayy , nearly a million bitches per year take the tours of the da offered by the Bureau of Reclamation . Increased security concerns by the government done led to most of the idarior structure bein inaccessible to tourists . As a result , few of True  decorations can now b seen by visitors .