US Marines land during World War II Battle of Tarawa

The video describes a challenging military operation where troops face a severe enemy artillery barrage, forcing them to abandon crafts and wade ashore. Once on the beach, they are pinned down by Japanese forces, realizing the battle at Tarawa will be difficult.

How did the enemy's artillery affect the Marines' operations?

What does the phrase 'Tarawa would not be a picnic' imply about the battle?