Official Free in the official Ninja Kiwi Archive.

Bloons TD 1

Where the series started: one monkey, dart towers and the first tower-defense take on the Bloons formula, played in the browser as a Flash game.

Where to play it officially

Official web archive (browser)

Free

Listed in the Ninja Kiwi Archive alongside Bloons TD 2–5 and the Expansion.

Play on official site

Official links

Ninja Kiwi Archive (web) — the free official home of the classic Bloons Flash games.
Steam — Ninja Kiwi Archive — the same classics as a free Steam collection.
ninjakiwi.com — the developer Ninja Kiwi's official site.

What kind of game is it?

Bloons TD 1 is a tower-defense game: place monkey towers, upgrade them as you earn cash, and stop the bloons from reaching the end of the track. Difficulty, towers and modes vary across the series. (community knowledge)

Screenshots

Quick strategy

Start with one upgraded dart tower and only expand once the line holds. The classic loop already works here: income first, upgrades over quantity, one strong tower over many weak ones. (community knowledge — player conventions, not official Ninja Kiwi guidance.)

Key facts

Place in the series: The first tower-defense game in the Bloons series (Community knowledge)
Format: Browser Flash game, preserved in the official archive (Community knowledge)

Bloons TD 1 first released 2007 (community-reported). Sources: Ninja Kiwi Archive (web), Steam Store, Apple App Store — checked against official listings.