The stream of ships heading to Gaza in defiance of Israel's blockade reflects the success of a pro-Palestinian group that's been creatively confronting Israel for years. High on victory, they are flush with new volunteers.

Activists of the International Solidarity Movement first sailed to Gaza in summer 2008 to challenge Israel's blockade of the Hamas-ruled territory. Most recently in May, it organized a Gaza-bound flotilla that led to a botched Israeli raid that killed nine activists, sparked an international outcry and forced Israel to ease its 3-year-old blockade.

In recent weeks, Israel has allowed more goods into Gaza.

"Around the world, we motivated people who were frustrated but didn't know what to do," said Huwaida Arraf, 34, co-founder of the ISM and its naval spinoff, the Free Gaza Movement, which organized the May flotilla. Since the movement's ships began, other groups have joined them or imitated them with their own ships trying to reach Gaza's shores — some of them successfully.

Israel is trying to crack down harder on ISM, and the group has also come under criticism for putting volunteers in danger.

Still, more people are volunteering.

Palestinian activist Hisham Jamjoum says the since the May flotilla, 10 recruits a week have attended his workshop, required for ISM volunteers — double the average.

The ISM was launched in 2001 for sympathetic foreigners to help Palestinians throw off Israeli rule. Its founders are a mix — Arraf, a Palestinian who is a dual Israeli-U.S. citizen; her husband, Adam Shapiro, an American Jew; Neta Golan, an Israeli, and Ghassan Andoni, a Palestinian from the West Bank.

Some 7,000 people — a third of them Jews — have participated since, mainly serving as peaceful, but provocative buffers between Palestinians and Israeli forces, mostly at protests. The group was first noticed in 2002 when its activists rushed past Israeli tanks to shield the besieged Palestinian leader Yasser Arafat in his West Bank headquarters.

The chance to participate in a compelling conflict is popular with college-age students on summer breaks. For many Jews, it's a chance to understand the conflict from a radically pro-Palestinian perspective.

But while most activists read about Mideast politics, volunteers can be clueless about conservative Palestinian culture. That's led to tensions, including sexual harassment. Some Palestinians assume female activists are permissive because they don't behave like conservative Palestinian women.

During last week's workshop, Jamjoum, 52, laid the rules out. He asked women to cover their arms and legs. For men: long pants only. Another volunteer explained how to dodge sexual harassment.

Jamjoum taught the volunteers Arabic phrases, including "please," ''thank you," and "I'm a vegetarian." Activists don't realize they are offending Palestinian housewives when they don't eat their chicken dishes, he explained.

Noting a Palestinian stereotype about unwashed "hippie" activists, Jamjoum told the girls makeup was OK. "Some people think to show solidarity with Palestinians, you have to wear ugly clothes. No. We like you nice and clean."

Upon graduation, an ISM dispatcher sends activists to demonstrations in coordination with Palestinian protest leaders. They distribute footage of clashes on YouTube, blogs and Facebook.

One ISM veteran — a 23-year-old American calling herself Saegan — highlights an activist's life. Like other volunteers, she would only identity herself with a pseudonym. During her 6 months with the group, she has been battered by tear gas alongside Palestinians, but also fended off a Palestinian man who tried to rape her while she slept in a West Bank village.

On a routine day, she joined a demonstration in the town of Beit Jala against Israel's West Bank separation barrier in June. The barrier protects Israel against militants — but also swallows chunks of Palestinian land.

Some 20 Palestinian youths and activists scrambled down an olive grove, where Israeli soldiers guarded a crane clearing land for the barrier. Soldiers fired tear gas. Palestinian youths hurled rocks. Saegan stood close Israeli soldiers. "You are stealing Palestinian land," she said.

To Israeli officials, the activists are misguided idealists and troublemakers. This year, Israeli forces stormed ISM offices three times, seizing equipment and arresting activists. In March, military officials broadened the definition of who is an "infiltrator," allowing them to speedily deport foreign activists.

The ISM takes its own measures: They don't keep databases, and activists use pseudonyms. Hardcore activists legally change their names to dodge an Israeli blacklist of ISM volunteers.

Stepping into confrontations can be dangerous. Rachel Corrie, 23, of Olympia, Washington, was crushed to death by an Israeli army bulldozer while trying to block it from demolishing a home in Gaza. A British activist was killed by an Israeli soldier in Gaza in 2003. A Palestinian ISM activist was killed by a Palestinian militant in the West Bank town of Jenin.

And the May flotilla went lethally wrong.

Israel says it responded with deadly force when activists on the ship — from a Turkish group that joined the ISM's flotilla — attacked commandos with iron bars. ISM activists weren't involved in the violence, but Arraf told Israeli naval officials that everybody was unarmed.

"They have become the useful idiots of Islamic extremists," said Israeli Foreign Ministry spokesman Yigal Palmor.

Palestinians have mixed views about their foreign friends.

Bassam Tamimi, a protest leader, complained activists often pressured Palestinians to stop hurling rocks at Israeli soldiers. Another leader, Shady Faraghwa said volunteers boosted morale. The volunteers say the Palestinian conflict is their emblematic issue — as explained by a 24-year old from Denmark who calls himself Carl: "This is the Vietnam of our generation."